SA urged to stay safe in the heat

South Australians have been urged to be vigilant in their efforts to keep cool as fears rise the heatwave across the state will claim lives.

Health officials say there have been no reports of deaths directly linked to the extreme conditions.

But chief public health officer Stephen Christley says there is a degree of inevitability that some people may succumb.

"If you look at what history tells us and the fact that there are vulnerable people in the community, then there's an inevitability that with some people, heat will have contributed to the fact that they will die during this period," Dr Christley said.

"When it comes to specific things like heatstroke, we would be hoping that the information people have and the rapid access to emergency services might be able to prevent those deaths."

Temperatures in Adelaide and across SA are set to hit record levels on Thursday.

Adelaide is forecast to have a top of 46C with some parts of the state likely to go higher as SA swelters through day four of the forecast five-day heatwave.

So far more than 100 people have been taken to hospital with heat-related conditions, slightly less than the during a similar heatwave in 2009.

The ambulance service says it is also receiving an extra 150 calls for help each day because of the weather.

Premier Jay Weatherill says people struggling with the heat should not be too proud to call for help.

"We are four days into what is expected to be a period of extreme heat," he said.

"There's a cumulative effect here that's going to present itself in threats to people's wellbeing."