The performance of NSW hospitals is down in several key measures, new figures show, despite the number of people seeking care remaining stable.

Longer wait times for patients in NSW public hospitals as well as pressure on ambulance services and operating theatres reveal a health system that is struggling to cope with demand, the Australian Medical Association says.

New figures released by the Bureau of Health Information for the January to March quarter show performance is down in several key measures, despite the number of people seeking care remaining stable.

Patients at hospitals are waiting longer for care, with fewer receiving treatment within the recommended time and one-in-three spending too long in the emergency department.

AMA NSW President Danielle McMullen says the data is proof the system is buckling under the pressure.

"It's like watching a car crash in slow motion," Dr McMullen said in a statement on Wednesday.

"Across the board, the five-year trends in activity and performance for emergency departments, ambulance services, admitted patients and elective surgical procedures all reveal a system that is struggling to cope with the current demand."

Just over a quarter of patients - 27.6 per cent - were not treated within the clinically recommended time, an increase of 1.7 per cent.

Fewer patients were in and out of the emergency room within four hours - either admitted, or treated and sent home - than in any other quarter over the past five years.

While the average time spent in the emergency room was just shy of three hours, a third of people spent more than four.

The NSW Nurses and Midwives' Association agrees the system is overwhelmed, saying it is leaving patients vulnerable and staff at risk of abuse.

"The amount of time critically ill patients are waiting for admission to a ward bed reinforces the absolute need to ensure our EDs (emergency departments) have at least one nurse for every three patients at all times," said the association's General Secretary Brett Holmes.

The number of elective surgeries performed was a five-year-record for the first quarter, up 14 per cent from the same time in 2020.

However, the average wait time for all categories of surgery - urgent, semi-urgent and non-urgent - increased and fewer people underwent their procedure in the recommended time frame.

The Bureau of Health Information notes backlogs created by the reduction in elective surgery during the pandemic likely played a role.

Paramedics in this quarter were also busier than they have been for five years, with the number of ambulance responses up by 1.7 per cent.

However, the percentage of the sickest patients seen by paramedics within 10 minutes was at its lowest for the quarter in five years - at two thirds.

The time taken to transfer patients from ambulance to hospital care also blew out.

Just over 15 per cent of patients waited more than 30 minutes to be transferred from an ambulance to the emergency room, the worst result in five years.

NSW Health Services Union secretary Gerard Hayes says it is evidence of ambulance ramping, a symptom of a severely underpaid and understaffed paramedic workforce.

"Paramedics are exhausted to breaking point," he said.

"There aren't enough of them."

The report comes after hundreds of NSW health paramedics, nurses and midwives last week undertook unapproved strike action to protest against unsafe work conditions and what they say is a paltry pay rise offer.

Opposition leader Chris Minns says the data demonstrates the need for serious money for health care in next week's state budget.

"The government has been putting money into bricks and mortar and capital in the health system, but we need new doctors, new nurses, new paramedics working on the ground," he told reporters.

"They need to be resourced."