Bushfire burning in SA

Firefighters expect to contain a blaze near Port Lincoln on South Australia's Eyre Peninsula as cooler conditions prevail on Tuesday.

The fire, which has burnt through at least 618 acres at Sleaford, was sparked by a burn-off designed to control invasive weeds, the Country Fire Authority says.

While yesterday's strong winds caught fire authorities and the weather bureau by surprise, the CFS said burn-offs were vital to prevent potentially devastating bushfires.

The blaze is not threatening properties but has closed the Lincoln National Park to new visitors.

It was sparked almost a week ago when a burn-off got out of control and flared on Monday.

It came as South Australia baked through a day of unseasonably high temperatures.

Adelaide reached 35.6C on Monday while Port Lincoln hit 37.2C.

Cooler conditions are expected on Tuesday as a cool change moves across the state.