Ambulance Victoria took the extraordinary step of telling people not to call triple zero unless it was an emergency on Monday night, as the mercury remained well above 20 degrees across the city.

At the time, paramedics were dealing with a high volume of non-urgent calls in metropolitan Melbourne and those patients were instead told to contact NURSE-ON-CALL or visit their GP.

Victorian Ambulance Union general secretary Danny Hill said the "massive surge" in demand led to up to 130 cases being left pending at its busiest point.

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"They went to what's called 'Code Red'," he told 3AW.

"That's the level of what we would have seen with thunderstorm asthma."

While all critically unwell Code 1 patients had their calls answered in a timely manner, many non-urgent Code 2 and 3 cases were provided care over the phone.

"This is a timely reminder to all Victorians to stay on top of their health this summer as the weather warms up and many of us re-emerge from stage three and four restrictions," an Ambulance Victoria spokesman said on Tuesday.

"We also encourage the community to check in with their GP and local pharmacist to ensure their medications are up to date."

Mr Hill said it was likely people had been unable or neglected to see their GP over the year because of the COVID environment.

"The flow-on effect is that things hit crisis point and people end up calling an ambulance," he said.

"You see that play out with massive amounts of cases."

Australian Associated Press