Hundreds of elective surgeries will be cancelled and a crisis control centre set up to manage an "unprecedented" nurses strike in Western Australia.
Nurses and midwives will walk off the job on Friday after voting to reject the government's latest pay offer.
The statewide strike is due to run from 7am to 9pm and include a rally outside parliament.
Health Minister Amber-Jade Sanderson says all category two and three surgeries for Thursday and Friday will be postponed.
Some category one surgeries are also likely to be impacted.
The state incident control centre will be activated to oversee the situation and deploy resources where needed.
Ms Sanderson delivered a scathing rebuke to the Australian Nursing Federation (ANF), which had encouraged its members to accept the latest pay deal before reversing its position.
"Make no mistake, this will have significant impact on patients," she told reporters on Wednesday.
"We are doing everything we can to ameliorate that impact."
Non-emergency outpatient appointments will be rescheduled or moved to telehealth, with oncology and dialysis patients among those affected.
Australian Nursing Federation WA state secretary Janet Reah has promised the strike will exclude emergency departments, intensive care units and acute pediatric care.
But Ms Sanderson said the union had demonstrated a "complete inability to manage their membership".
"They have admitted they don't know how many people will be walking off, they don't know where they will be coming from," she said.
"That is very unusual for a union not to have that kind of information.
"There are women who are due to give birth on Friday. There are women who are due to be induced on Friday or come in for an elective (caesarean).
"We will do everything we can to make sure you can birth safely in our public health system."
Ms Reah on Wednesday said the government had no intention of negotiating and hit back at suggestions patients would be put at risk.
"Of course they'll be looked after. That is our job," she told reporters.
"Nurses do not want to strike, they want to be paid fairly, they want reasonable workloads. This government keeps annoying the nurses and escalating things further."
Department of Health director-general David Russell-Weisz said about 650 elective surgeries were booked across WA on any given day, including 250 category one procedures and about 14,000 outpatient appointments.
Nurses and midwives have been offered a three per cent annual pay rise, a one-off $3000 bonus and the introduction of nurse-to-patient ratios.
The union is now pushing for a five per cent pay rise, having previously flagged it would compromise on pay if ratios were brought in.
"The challenge the government has is we can't take the ANF for its word. They haven't been able to get things over the line," Ms Sanderson said.
Only about 4800 union members took part in the vote to reject the latest pay offer, representing less than a quarter of the state's nursing and midwifery workforce.
