SA Health on Tuesday afternoon announced urgent category two and three surgeries in public hospitals would be cancelled for Wednesday and Thursday, and would likely only resume after the Easter long weekend.

Chief executive Robyn Lawrence said the step was necessary as the state's hospital and ambulance systems had been experiencing very high demand in the past few days, which was expected to continue across the weekend.

"This decision was based on the needs of the system, and to ensure that we can provide appropriate emergent care to those who need it, and beds over the Easter weekend," she told reporters on Wednesday.

Category one surgeries will continue as planned.

"We have every single bed open," Dr Lawrence said.

"So we're not constrained in our capacity by staffing levels - what we're seeing is more people requiring hospital admission and requiring longer hospital admissions."

The announcement came after ramping hours reached record levels in the past two weeks, the head of SA's ambulance union said.

"And that was having a significant impact on ambulance response time through emergency cases," AEA secretary Leah Watkins told ABC Radio on Wednesday.

"There does need to be more work done so that we don't end up in this situation again."

SA doctors' union SASMOA said it first raised concerns about increasing pressures on the hospital system two weeks earlier.

"It was quite clear at that point that there were really extraordinary circumstances facing the frontline health workers in our hospitals across the system," Bernadette Mulholland told ABC Radio.

"There are extraordinary pressures going across the system in all of our hospitals which was causing quite frantic concerns for our medical staff."

Dr Lawrence said as demand mounted in recent weeks, individual local health networks could cancel non-urgent surgeries to free up capacity, but it was not until Tuesday that the decision was taken to cancel elective surgery across the entire system.

Opposition health spokeswoman Ashton Hurn said people desperately waiting for elective surgeries have had the "rug pulled out from under them".

"There's nearly 19,000 South Australians who are waiting often in agony and often for months on end for elective surgery," she said.

She said it was a big coincidence the "abrupt" cancellation had occurred days after the Dunstan by-election, which the government appeared to have won by the barest of margins as final votes continued to be counted.

"This would absolutely have further exposed the significant pressure that our health system is under here in South Australia," Ms Hurn said.

"Would it have changed the result of the Dunstan by-election?

"Ultimately, we'll never know."

Premier Peter Malinauskas bristled at suggestions the announcement was delayed for political reasons.

"You're an intelligent man," he told ABC Radio presenter David Bevan when the question was put to him.

"And your profession is to engender huge degrees of cynicism within your audience towards the government of the day.

"Sometimes that's a virtuous exercise, sometimes it is completely unfounded and contrary to any evidence or facts whatsoever.

"And this is an example of that, David."

Australian Associated Press