Victoria's embattled triple-zero call service resorted to manually allocating ambulances when a technical error crashed its system overnight

More than 70 patients were left waiting for paramedics after the dispatch system suffered an IT glitch that caused another "code red" emergency.

"That's a sign of a system that's very much under strain when we've got that many cases pending," ambulance union secretary Danny Hill told Melbourne radio 3AW on Friday.

The fault was resolved within 30 minutes, an Ambulance Victoria official said.

The dispatch system used by the Emergency Services Telecommunications Authority pinpoints the nearest available ambulance to send to a medical emergency.

When it crashes, call-takers have to resort to a pen and paper-type system with crews manually calling in their locations over radios, Mr Hill said.

"It's inefficient. It means that crews are often not the nearest crew that might be dispatched to a case," he said.

All code one cases - reserved for the most serious emergencies - were dispatched appropriately and the IT fix ensured there was minimal impact on ESTA's service to the community, a spokesperson said.

A string of recent deaths in Victoria have been linked to ambulance delays stemming from ESTA system failures, with a Melbourne law firm flagging a potential class action lawsuit.

The IT glitch occurred in the midst of enormous demand and resulted in the code red for up to two hours, senior state minister Martin Pakula said.

Ambulance Victoria experienced its busiest quarter in history from January to March and Mr Pakula said the current pressure on the health system was undeniable.

Mr Pakula spruiked the government's pledge to recruit and train 400 ESTA staff as part of a $333 million budget spend, after a review found "continued and systematic underperformance".

The CAD system relied on "monolithic architecture" and would not meet future needs of staff, emergency organisations or the community, it said.

A new system being implemented will shift services to the cloud, reducing reliance on the current platform.

In his review, former Victoria Police boss Graham Ashton recommended moving the service into the Department of Justice and Community Safety and rebadging it as Triple Zero Victoria.

ESTA's benchmark is for 90 per cent of ambulance triple-zero calls to be answered within five seconds.

The CAD system will continue to fail if capacity isn't immediately increased, opposition emergency services spokesman Brad Battin said.

"They expect a response within five seconds. The longer the delay, the more chance of someone dying in Victoria," he said.

"We need to fix this crisis and we need to get it done as soon as possible."