SA Premier Steven Marshall said there had been a "significant deterioration" in Australia's fight against the virus and so the state would close its border to Queensland, WA, the NT and the ACT effective immediately.

"I think South Australia now needs to take decisive action to make sure we can continue to keep our state safe and our economy strong," Mr Marshall said on Sunday.

The state will keep its existing hard border with NSW excluding anyone from within 100 kilometres of the NSW border. All Victorians will now need to be tested for the virus on the first day they arrive in SA. There remains no restrictions for travellers from Tasmania.

Mr Marshall said he would announce on Monday whether there would be further "internal restrictions".

"We're thinking of moving for a higher level of restrictions internally in South Australia for one week period," the premier said.

"This would address things like the numbers at home gatherings, the density arrangements, the mask wearing, particularly in aged care, and also in other settings where there may be vulnerable sites."

Chief health officer Nicola Spurrier stressed that vaccination was the best way to stop the spread of the virus in the community.

"If you had been sitting on the fence a bit about whether to get your vaccine or not, it is the time to get off that fence and roll your sleeve up and get vaccinated," Professor Spurrier said. "It is incredibly important. We are quite vulnerable at the moment."

Prof Spurrier confirmed there were nine active cases in the state and that there had been an increase in tests.

Australian Associated Press