The local unit hit an intraday low of US89.90¢ in late afternoon trade, and experts warned that if a significant slide starts it could be difficult to unwind.

Monday's new low point follows the Aussie's largest five-day fall last week - from around US94¢ - since November last year.

Although not discounting a rebound, economists have begun noting that the currency's movements are now more closely tracking changes to basic economic indicators, such as the price of iron ore and coal, which together account for about one-third of Australia's export revenue.

Weaker-than-expected production and electricity-usage data from China also weighed on the Aussie over the weekend, while any signals of interest rate rises or faster-than-expected withdrawal of economic stimulus by US Federal Reserve this week will also push the greenback up against the local unit.

In a quiet week for local data, the results of the Scottish referendum on independence from the United Kingdom will move pounds sterling either sharply higher or lower against a range of currencies, including the Australian dollar.

The Aussie has fallen sharply again the pound in recent days, after climbing to a year-to-date high, of 57.6 pence, against the UK currency just over a week ago. That was on the emerging possibility of Scottish independence. On Monday afternoon the Aussie was fetching 55.4 per pence.

If the dollar stays below US90¢, it will eventually take pressure off the Reserve Bank of Australia to lower interest rates.

The RBA has been caught between wanting to ease to address the strong currency and slowing economic growth and the need to avoid oveheating house prices by keeping interest rates too low.

Whether or not the Aussie drops below US90¢ and stays there will depend increasingly on fresh volatility in the currency markets, and at what point the risk to foreign investors of a sustained fall outweighs the benefits of the higher yields available on Australian bonds and other assets.

"A persistent surge in expectations for large swings amongst the major currencies would make the Aussie's relatively small yield advantage a much less attractive - and riskier - proposition," market analyst at FXCM David de Ferranti said on Monday.

He said this could open the door to the mass unwinding of carry trades, where investors effectively borrow in a low-yielding currency and invest in high-yielding assets in another currency.

Because of the build-up in these sorts of positions, "once the floodgates open, they may be difficult to close".

"It will be difficult for the Aussie to recover back above the US92¢ level, which is significant from a technical standpoint," he added.

"We are teasing at a push below US90¢ today which, if broken, would cast the spotlight on the US89¢."

According to data released by ANZ on Monday, leveraged investors such as hedge funds cut their long term bets on a higher dollar by $US700 million in the week to September 9, with further unwinding noted after the survey period.

Over the long term, a lower dollar will also help Australian businesses which have laboured to compete with lower-cost producers from other countries.

Indeed, a falling dollar has many implications for Australian companies and for the local sharemarket, CMC Markets chief markets analyst Ric Spooner said.

"While weaker-than-expected data from China will have investors cautious about resource stocks, a falling Australian dollar could easily see ongoing weakness in the banks as offshore investors head for the exits," he said.

Company valuations could be hit by a lower Australian dollar, and "for international investors there may also be some concern about the implications of weaker Chinese growth for the broader Australian economy", Mr Spooner said.

Investors hoping to take advantage of the effects of a lower Australian dollar might be better of waiting until falling stock prices make shares better value, he said.

Australian industries that should benefit from a sustained drop in the local unit include farmers, whose exports often have to compete with lower-cost producers from other countries, and agribusinesses such as wine and processed food.

Domestic suppliers forced to compete with low-cost imports also do well out of long-range dollar weakness.

Banks, which raise money in international markets and then lend in Australian dollars, will also be able to add a few basis points to their margins if the Australian dollar continues to fall and stays lower.

"Obviously, you need to raise less foreign currency-denominated debt to get converted to an equivalent amount of Australian dollar debt," JP Morgan banking analyst Scott Manning said.

Over the shorter term, he said, Australian banks would also benefit from the sudden change in the amount of collateral they have to hold against interest rate hedges.

"When Australian banks issue debt offshore, they effectively swap it back into Aussie dollars at the time of the deal so they don't take currency risk," he said.

Collateral is posted against those derivative trades.

As the Australian dollar weakens against the currencies in which banks are raising finance, it is the counterparties who have to post more collateral. The banks make extra money out of this collateral.

"So there is a modest positive benefit to net interest income," Mr Manning said.

The Australian Chamber of Commerce and Industry said the fall in the dollar would assist exporters and import-competing businesses. For other businesses, however, it would lead to extra costs.

"Australian manufacturers did it really tough earlier in the year during a sustained period when the dollar was high," said ACCI's chief executive Kate Carnell. "It is pleasing to see some relief for them."

"But for other business is a different story."

Ms Carnell said the fall could be bad for businesses not exposed to international competition. "For these businesses, the fall in the dollar means increased prices for key inputs such as fuel and also makes imported capital more expensive," said Ms Carnell.

Ms Carnell said the fall in the dollar would put upward pressure on inflation, but she urged the Reserve Bank to keep rates on hold.

"We are just starting to see some green shoots of growth in the broader economy and any move to lift interest rates at this stage risks snuffing out the transition towards broader-based economic growth," she said.

Retail groups welcomed the fall in the dollar. "The consensus is the lower the dollar goes, the better for Australian retail in all its forms," said Paul Greenberg, executive chairman of the National Online Retailers Association.

Mr Greenberg said that, currently, about 25 cents in the online Australian shopping dollar was spent overseas. A falling Australian dollar, said Mr Greenberg, meant consumers would start spending more in Australia.

"The theory is that once it goes below 90 or even towards 80 US cents we'll start looking at greener pastures on our own doorstep. We would welcome a softer dollar, it's definitely been high for a long time."

But Mr Greenberg warned that consumers would have to fork out more for imported goods with a lower dollar. "A lower dollar doesn't automatically mean we'll have happy days domestically," he said. "Everything is manufactured in China and we have to import everything from China."

The executive director of the Australian Retailer's Association, Russell Zimmerman, also welcomed the falling dollar. "From a retailer's perspective it's good because as the dollar falls it makes us more competitive with overseas online retailers," he said. "It will be a good thing if it remains low."

Mr Zimmerman conceded that some retailers who depended on selling imported goods would suffer. "There will be a problem for some retailers who have lived off the high dollar and used it to support their profit margins," he said. "If the dollar falls they'll need to reconsider their structure a little bit.

"But, generally speaking, it will be it will better for the general retail economy."

For tourism operators, the advantages of a falling domestic currency are not as easy to predict.

Although the relative weakness of a currency can make a country more attractive to foreign visitors, travellers tend to book well in advance and make their decisions based more on the affordability of airfares than anything else.

Once in the country of choice, visitors adjust their day-to-day spending on food, tours and other variables according to individual budgets.

According to Accor's chief operating officer for the Pacific region Simon McGrath, it would take a while for somewhere like Australia to lose its reputation as a high-cost destination.

"If the dollar were to stay lower over a couple of years, then Australia would reset as a cheaper destination," he said.

Domestic travellers, meanwhile, are more likely to take their holidays at home as their currency weakens, although this, too, takes a while to become entrenched.

Tourism Australia managing director John O'Sullivan said a weaker exchange rate would encourage foreign tourists to spend more in Australia. "We're trying to get the industry to $115 billion in overnight expenditure by 2020," he said. "We're currently at $83 billion."

However, Mr O'Sullivan said he didn't expect a changing dollar to affect the numbers of foreign visitors coming to Australia. "Even though we've had the dollar at a high rate we've still got record numbers of arrivals over the last year, rising about 8 per cent," he said.

He added that the dollar was not a crucial factor for Australians when determining their holiday destination. "It's one of the factors but it's largely related to consumer confidence and the appeal of a destination," he said.

Flight Centre spokesman Haydn Long said the overall impact would be minimal for Australians travelling overseas.

"For most people it's irrelevant. A lot of people are travelling to Fiji, Thailand, Bali, New Zealand, the UK or Europe and the US exchange rate is completely irrelevant for them," he said.

For travellers who are affected by the US exchange rate, "they just downgrade their plans. They might stay for 10 days instead of 2 weeks or at a 3-star instead of a 4-star. They don't change where they travel to."

Tony Mahar, the National Farmers Federation general manager of policy, said any reduction in the Australian dollar was welcome. "It makes our products more competitive on the global market which is where two-thirds of our products go," he said. "It's not a panacea for high production costs but it will help companies to source global supply chains."

Mr Mahar said the dollar was still too high but he declined to specify a preferred level. "There's probably a band between 75 and 80 cents where it probably fits with most commodities," he said. "But it's hard to put a specific number on it."

The International Education Association of Australia, which helps to market Australian tertiary education overseas, also welcomed the lower dollar. "The international education industry strongly welcomes the Australian dollar's decline," said national executive director Phil Honeywood. "We are now facing stiff  competition from countries such as Canada, the United States and New Zealand which are more actively competing against Australia for international students than ever before," said Mr Honeywood.

For every one cent decline in the Australian dollar we get a tangible increase in students, particularly as we have high costs for living expenses, accommodation and so on. Parents are becoming much more price-sensitive when they make their investment in education for their child to come and study abroad."

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