Residents at Finniss south of Adelaide have assessed the damage left by a fire which burnt 300 hectares of land during Friday's extreme heat.

The fire broke out about midday and spread rapidly through crops, farmland and vineyards.

The blaze also destroyed a kilometre of rail tracks, forcing the historic Steam Ranger to cancel services in the area until further notice.

Fire authorities responded swiftly in the hot conditions with the temperature at nearby Victor Harbor reaching 43.8 degrees Celsius.

Many residents stayed to protect their properties and the cause of the blaze is still being investigated.

Water bombers were used to douse the flames and about 60 firefighters brought under control on Friday night.

Some residents received text messages from the Country Fire Service alerting them to the fire but one local says he did not receive it until an hour and a half after it started.

Local vineyard manager Mick McDade says he was surprised by how fast the flames spread.

"How quickly it moved was amazing... once it got to the treetops it was just shooting across," he said.

"Then just to see how much devastation to the vineyard, burning posts, dripper lines and stuff like that, never seen anything like this before in my life."

The CFS has warned residents to be careful of falling tree limbs in the area.

Another blaze near Sevenhill in the Clare Valley has also been controlled.

CFS firefighters will continue to monitor the two fires ahead of further hot weather expected in the coming week.

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