South Australians have endured one of the state’s hottest starts to summer with temperatures reaching the high 30s and low 40s.

Fire crews remain on high alert as the heatwave, which is expected to continue until Monday, grips the state.

Total fire bans are in place for six districts, with extreme fire danger forecast for the West Coast.

By early afternoon Adelaide had reached 39.5 degrees Celsius, while towns in Flinders, Mid North, North West Pastoral and North East Pastoral areas recorded temperatures in the lows 40s.

At 2:30pm Ceduna hit 45.3C.

The mean maximum temperature for Adelaide in December is 27.1C.

Thousands of people have braved the heat for the Stereosonic music festival at Bonython Park.

SA Police said a number of people had been treated by first aid volunteers for heat and alcohol-related issues during the first few hours of the event.

Country Fire Service’s (CFS) Phil McDonough said crews would be keeping a close eye on the Pinery fire ground over the coming days, to ensure there were no flare-ups.

“There is an increased fire danger over that area,” he said.

“Local crews are continuing to patrol and mop-up and respond to anything that does occur in those areas and that will be maintained over the next few days.”

The Pinery fire burnt more than 85,000 hectares of land, destroyed 87 homes, killed two people, tens of thousands of livestock and razed more than 300 farm sheds and outbuildings.

He warned the weather was creating increased fire risks across the state and noted Monday was “probably the worst day of the lot”.

The weather bureau has forecast high temperatures for Monday, with possible showers.

Bureau of Meteorology senior meteorologist Darren Ray told 891 ABC the weekend’s heatwave was “pretty unusual”.

He noted the last time the state had seen “runs of days in the high 30s” at the start of summer was November 2009 and in 1908.

“We’ve come out of a pretty warm spring where temperatures were quiet a bit warmer than average and rainfall was about half the average,” he said.

“We are seeing a pretty unusual burst of heat for this early coming through spring and into summer.”

He forecast “spikes” of hot weather throughout summer and tipped the next one with be around Christmas.

Mr Ray said January was “not looking to be a super hot month” but February would be dry and warm.

Meanwhile, three CFS has already attended several small grass fires and crews remain at a haystack fire at Woolumbool in the state’s south east, which is believed to have caused about $1 million in damage.

The fire broke out early this morning and has destroyed 1,000 tonnes of hay.

CFS crews and farm fire units have contained the fire and smoke is visible in the area.

Sporting events reviewed due to extreme heat

Meanwhile, there has been a review of sporting events across the state due to the heat.

Football Federation Australia has agreed to push the starting time for W League and teams back by two hours due to the weather forecast.

The W League match will now start at 4:30pm and the A League at 7pm.