While the ambulance union said the outage was a major issue which caused communication delays, Ambulance Victoria and the Emergency Services Telecommunications Authority said there were no issues.

Ambulance Employees Australia of Victoria secretary Steve McGhie said radio broadcasts went offline at about 11am.

He said paramedics had relied on a paging system and personal mobile phones to receive job information.

"I've just been informed it is still down," he said about noon. 

"I've been told there's no redundancy provision. 

"They're using an old base radio that they've plugged into a power point and they're talking to ambulances as if talking car-to-car.

"It does cause delays in response times, but at this stage there's been no adverse outcomes with cases."

Mr McGhie said the service was back online after about three hours.

But ESTA head of corporate affairs Rosie Mullaly said the union had spread unnecessary fear about the Triple-0 service.

She said the service had remained operational using a back-up radio system, and said the paging system still worked.

"For the union to raise this to frighten the community around the operation of the Triple-0 service is just irresponsible," she said. 

"The primary system is the paging.

"They're using an alternative radio channel or system. 

"But absolutely, the service is still operating. 

"There is no impact on anyone calling Triple-0 and no impact on us dispatching jobs." 

A Telstra spokesman said a contractor had cut through a fibre optic cable at Ballan near Ballarat, which was still being repaired late yesterday. 

Ambulance Victoria communications and referral manager Danny McGennisken said the dispatch system had gone offline.

“There was a 15 minute outage to one rav-net rural dispatch radio channel affecting the Hume and Loddon Malle regions Thursday morning,” he said.  

“Crews were still able to be dispatched to cases by pager, and they were able to contact our dispatch centre by phone.

“An investigation is underway into the reason for the outage.”

The ambulance union and state government have battled over wages since mid-2012.

Mr McGhie said raising the outage as an issue was not related to the discussions.

“It has nothing to do with the EBA,” he said.

“This is a  system in crisis.

“This is about another communications issue that puts paramedics and the public at risk.

“The system has gone down several times in the last six months.”