Ambulance union secretary Steve McGhie said there was no available ambulance between Ballarat and Nhill between 8pm and 8.30pm.

"Paramedics in the Wimmera have put up with a lot of stress and strain and we saw on Monday night that there was no ambulance between Ballarat and Nhill," he said.

"The potential outcome is that a patient could have died.

"The government has to get this sorted out, it was sheer luck nothing happened."

Ambulance Victoria Grampians regional manager Greg Leach did not confirm or deny the absence of an ambulance from the region during the time.

"We always prioritise our ambulances to respond to the sickest patients first, particularly those with life-threatening conditions, and are not aware of any delayed responses or service delivery issues occurring during this period," he said.

"To provide the best possible spread of ambulance resources throughout the region, we arranged rendezvous points for Wimmera ambulances to meet other crews and complete patient journeys to Ballarat."

Mr McGhie said the government needed to act immediately to increase services in the interests of patient safety.

"There's no question it's about resourcing," he said.

"What else can it be when you have more than 270 kilometres, three hours travelling time and you don't have an ambulance available?"

He said the union made a submission to Ambulance Victoria in February, which asked for 267 new paramedics to be deployed throughout the state in the next 12 months.

The submission nominated Horsham as a location for extra services.

Service shortages come as union members voted to intensify industrial action in their 20-month pay dispute with the government.

More than 98 per cent of paramedics surveyed voted for increased action.

Action beginning tomorrow night at 7pm will allow journalists, media presenters and politicians to go out on ambulances to observe paramedics' work.

Mr McGhie said further industrial action, including strikes, could be taken if the dispute failed to reach a resolution.

"The most extreme work ban is a stop-work meeting, but we would be hopeful it doesn't get to that," he said.

Mr McGhie said he was concerned about the results of a survey of paramedics, which showed 55 per cent planned to quit in the next five years.

"If those figures are reflected across the state you could potentially lose half the workforce in the next five years in the Wimmera," he said.

"The government says it will employ more people to make up for it but you would still be losing the experience base, which is fundamental to making sure the ambulance service is running effectively."