Bushfire smoke heading for SA mainland

Smoke from the Kangaroo Island bushfires will posing a serious health risk as it blankets wide areas of South Australia, authorities say.

SA Health said the level of smoke from early on Friday would be higher than previously experienced.

This could pose a serious threat to health, particularly for vulnerable people with lung or heart conditions, the department said.

"We are urging people to stay indoors where possible, avoid physical exercise outdoors and reduce their exposure to smoky air," Chief Public Health Officer Nicola Spurrier said.

"People should keep windows and doors shut, and ventilate the house once the smoke clears.

"Smoke particles can aggravate existing health problems such as chronic bronchitis, emphysema, asthma and heart conditions."

On Thursday night, Adelaide's air quality was already rated as poor by the Environment Protection Authority.

Some regional areas, including the Spencer Gulf, were rated as very poor.

The smoke warning came after the bushfires burning on Kangaroo Island escalated significantly on Thursday afternoon, threatening the towns of Parndana and Vivonne Bay.

For the first time, a watch and act warning was also issued for people on the outskirts of Kingscote.

SA Health said the worst of the smoke across SA was expected to clear around lunchtime on Friday.