NSW Ambulance was forced into an emergency "status three" case load declaration on Monday, prompting the union to call for 1500 more paramedics.

The union for NSW health workers has refused to rule out industrial action after the state's ambulance service became so busy that paramedic managers, educators and trainees were forced to work on the front line.

At one point on Monday afternoon, only 14 ambulances were available to cover 61 triple-zero jobs in an area stretching from Sydney's northern beaches to Bowral in the Southern Highlands.

NSW Ambulance said it had also received more than 400 triple-zero calls in a two-hour period on Monday.

This prompted NSW Ambulance to enter emergency "status three" mode for about 30 minutes when paramedic managers, educators and trainees were summonsed to perform frontline jobs.

Health Services Union secretary Gerard Hayes told AAP that Monday's shortage was down to a lack of paramedic personnel, rather than a shortage of ambulances or other infrastructure.

The HSU is surveying its members and will make a decision on potential industrial action by week's end.

"They are so overwhelmed they can't effectively run a service," Mr Hayes said on Thursday.

The HSU will campaign for an additional 1500 paramedics to be included in this year's NSW budget.

NSW Labor health spokesman Ryan Park backed the call, saying wait times for emergencies have blown out in some cases to nearly 45 minutes.

Mr Hayes said 750 additional paramedics were promised two-and-a-half years ago, which he considered insufficient at the time and even more so now.

Only more government funding could unblock the pipeline connecting paramedic university graduates to full-time paramedic jobs, with barely a third of current graduates nationwide being employed.

"What's important here is that these are young people who have trained and developed HECS fees, these are specialist qualifications," Mr Hayes said.

"(Yet) they may need to go back to university, look at doing something else."

NSW Ambulance said it would soon deploy 100 of the 750 previously-announced new paramedics ahead of schedule, and the government had spent $184 million on critical ambulance infrastructure.

"Like our hospitals, NSW Ambulance has contingency plans in place to respond to sudden surges in activity," the service said.

In the last quarter of 2020, there were close to 320,000 ambulance responses - the highest since the NSW Bureau of Health Information began collating the data.

Australian Paramedics Association NSW president Chris Kastelan said Monday's "status three" was the second such designation in NSW in a fortnight, and paramedics were fatigued and overworked.

"Paramedics are concerned that these extraordinary measures are becoming normal - we have been hitting 'status two' most weeks," he said in a statement.

"If we are already running our ambulance service at breaking point on a Monday afternoon, what is going to happen as case load picks up with the winter influenza season, let alone further COVID-19 outbreaks or natural disasters?"