The Emergency Services Telecommunications Authority on Thursday issued a statement saying chief executive Marty Smyth had resigned to "pursue new opportunities" in Queensland.

Former Victoria Police assistant commissioner and current ESTA board member Stephen Leane will serve as interim CEO until a replacement is found.

ESTA provides Victoria's 24-hour emergency call-taking and dispatch services for ambulance, fire, police and the Victoria State Emergency Service.

It has been under sustained pressure amid the pandemic, with demand increasing by more than a third in recent months as COVID-19 cases have risen.

Earlier this month Mr Smyth said the average wait time for people calling the service was one to two minutes, well above the target of five seconds for ambulance calls.

Last week, the Victorian government announced former police commissioner Graham Ashton would lead a review of ESTA after two people suffering cardiac arrest died with triple-zero calls going unanswered for five minutes in each case.

A toddler earlier died after suffering a cardiac arrest. Her family waited on hold to triple zero for one minute and 41 seconds.

It is not yet known whether the delays contributed to the deaths.

The government is also relaunching its 'Save Lives, Save 000 for Emergencies' campaign to reduce the number of non-emergency calls to the service.

More than one in five calls to triple zero for an ambulance do not require an emergency response.

Opposition spokesman for emergency services Brad Battin said it was the "worst possible time for chaos and instability within ESTA".

"People are dying on hold and there are no excuses. Daniel Andrews has failed to deliver the additional resources our emergency services were always going to need," he said in a statement.

Australian Associated Press