Thousands of nurses across New South Wales have walked off the job demanding better pay, despite an Industrial Relations Commission (IRC) order for them not to.

On Monday, the industrial court told the nurses' union to call off the 12.5-hour-long strike.

The state government argued the strike would cause extensive delays at hospitals, impacting patients and delaying elective surgeries.

However, the Nurses and Midwives Association said its members walked off the job at 7am as part of their fight for a one-year, 15 per cent pay rise.

Speaking to a nurse who called into Nine Radio, Premier Chris Minns said his government could not afford to meet the union's demands.

"If we implemented a 15 per cent, one-year increase in salaries, it would cost $6.5 billion, that's more than we spend on the entire police force," he told 2GB.

"I think police, teachers, corrections officers, paramedics would rightly knock on my door the next day and say we want 15 per cent as well."

The Minns government offered NSW public sector workers, including nurses, a three-year 10.5 per cent pay rise.

"I understand that's [10.5 per cent] not be acceptable, but the government has said if we can't get to an agreement on our offer, we're prepared to accept the decision of the independent umpire," Mr Minns said.

'We remain at the table'

During a budget estimates hearing, Health Minister Ryan Park came under fire from Liberal MLC Natalie Ward for having not resolving the wage dispute sooner.

Mr Park apologised, but said the government and union had been left in a difficult situation due to the previous government's public sector wage cap.

Mr Park he was "disappointed" the strike went ahead before an organised meeting with the union on Thursday.

"I've got a health system that I have to run, and it is disappointing that they are taking strike action today," he said.

"We remain at the table. I'm not pretending we've got a deal yet, because we haven't."

Mr Park said he remained "committed" to continue discussions with the union this week.

"We will continue to engage," he said.

"Have we got a deal yet? No. Can we pay the 15 per cent in a single year? No, we can't. Have we made progress on other things that the nurses and midwives have campaigned for over 20 years on? Yes, we have."

Nurses strike outside premier's office

Scores of nurses took to the streets outside the premier's electoral office in Kogarah and state parliament, brandishing signs and flags.

One nurse, who only wanted to be identified as a branch member at Sutherland Hospital, said she felt "let down" by the Minns government.

"We have endured spitting, punching, kicking, swearing insults .. the Labor government was elected on a promise of supporting nurses and midwives," she said.

She said the 10.5 per cent offer put on the table by the government was a "disgrace".

"If we were men, we wouldn't be having this conversation," she said.

"This is a gender pay gap that needs to be addressed."

Life-preserving staffing is expected to be maintained in public hospitals.