Adelaide has gone from setting summer heat records to having its wettest day since 1969, with emergency services issuing a Watch and Act message on Friday about the risk of widespread flash flooding.

The latest wave of extreme heat ended in the past day, when rain swept in.

The State Emergency Service says heavy rain across the Mount Lofty Ranges and the state's mid-north mean there is an elevated risk of flash flooding.

Flooding has been reported across the city on Friday and many roads became chaotic as they turned into deep streams and became gridlocked with traffic.

Rail boom gates were stuck in several locations, including on busy South Road, leading to enormous traffic jams.

At Woodville, in the north-west suburbs, the deep waters on Port Road caused major problems.

Emergency services have dealt with hundreds of calls about flooding across most parts of the metropolitan area.

Saint Andrews Hospital in South Terrace in the city was forced to cope with sudden floodwaters and an underground car park there was evacuated swiftly, preventing cars from disappearing under the rising water.

On Friday, the residents of Mary Street in suburban Peterhead were busy putting sandbags around their properties to try to keep out the rising waters.

Fire crews arrived and helped pump some of the water away from the houses.

But Ben Barnett said his house did not fare well.

"My wife woke up this morning, went down to the lounge room and stepped down and the water was up to her ankles," he said.

"We have a pond in the backyard so all our goldfish are swimming around in the backyard."

Also in Peterhead, Neil Gibbens said his young daughter's room flooded, then the trouble spread.

"As we tried to stop that, the water is coming around the back, so our kitchen is flooded," he said.

Creeks burst their banks in several suburbs, including at Mawson Lakes in the north.

Adelaide's total rainfall since the deluge began had exceeded 90 millimetres by Friday afternoon.

Rain rewrites the weather records

Rainfall for 24 hours to 9am Friday. ( Bureau of Meteorology )

It has been the wettest 24-hour period in Adelaide since 1969 and the fifth-wettest Adelaide day on record, with Adelaide officially recording 75.2mm in the 24 hours to 9:00am Friday.

In the same period, Lenswood in the Adelaide Hills got a 110mm soaking, and some suburbs were wetter than the weather bureau's official reading. Kilburn had 97mm of rain and Port Adelaide 84mm.

Senior weather forecaster Mark Anolak says a large part of South Australia was getting the heavy rain.

"Northern Eyre Peninsula, the mid-north, northern parts of the Mount Lofty Ranges and the Adelaide area itself. Also into the Murraylands and Riverland districts," he said.

Sorry, this video has expired From record heat to record rain in Adelaide ( John O'Shea )

"We're expecting a band of very heavy rainfall through there and wouldn't be surprised to see 50 to 100 millimetres through that band."

On the west coast, houses at Streaky Bay were flooded as 109 mm of rain fell in 24 hours.

A bushfire has been burning for more than a month in the southern Flinders Ranges but firefighters were still waiting for help from the rain on Friday.

The weather bureau said just 2mm had fallen in the fire zone but there was a prospect of about 20mm before the day was out.

The fire earlier was contained and by lunchtime on Friday the Country Fire Service finally said it was under control.