South Australian Premier Steven Marshall has announced the state's borders will be closed from 4pm on Tuesday, following similar moves by Tasmania and Northern Territory.

"We do not make this decision lightly, but we have no choice," Mr Marshall said at a press conference, which followed an emergency meeting of the state's cabinet.

"We make this decision in the interests of public health," he said.

"What we are trying to do here is massively reduce the peak of the coronavirus impact and push it out into the future as far as possible."

Anyone entering South Australian, including returning residents, state will be forced to self-isolate for 14 days, and inform police where they will be. Road crossings and the airport will all be monitored.

SA Police will be staffing 12 border patrol stations.

The South Australian government believes many of its confirmed cases have come from interstate, and this decision will "turn off the tap".

"This is no longer something which is optional," Mr Marshall said. "It is mandatory. It is the social responsibility of every single person in this state to make sure

Freight and vital goods will still be allowed across the border.

It comes amid reports that NSW and Victoria are agitating for the National Cabinet to tonight extend lockdowns to all non-essential services, with potentially dramatic impacts on jobs and businesses.

Such a move could also result in schools being shut in those states this coming week.

Originally published as South Australia closes borders