Police hold 'grave concerns' as search for missing plane enters fourth day

The search for the married couple, a man in his 70s and a woman in her 60s and their dog entered a fourth day on August 5, focusing on Tasmania's coastline.

A Tasmania Police helicopter crew is searching the northern coastline between George Town and Turner's Beach, with marine vessels grounded due to poor weather conditions.

The bright-green twin-seat light plane took off from George Town Airport at around 12:45 on August 2.

There has been no communication from the aircraft or the couple since then.

Family members raised the alarm after the aircraft failed to arrive at its central New South Wales destination.

Extensive searches involving the Australian Maritime Safety Authority Challenger jet and Tasmania Police helicopters and marine vessels followed, but have yielded no sign of the couple or their plane.

Tasmania Police Northern Commander Marco Ghedini said the police are concerned for the missing couple.

"As we enter the fourth day of searching, police hold grave concerns for the missing couple," he said.

Commander Ghedini said a further assessment of the search will be made in the coming days.

Police have asked anyone with information that could assist the search, such as a plane matching the description, or anyone who has noticed any unusual debris on land or in the water, to contact Tasmania Police on 131 444.