South Australian authorities are not ready to lift border restrictions with NSW but have moved to ease some local COVID-19 restrictions.

South Australia will keep its COVID-19 border restrictions with NSW in place but has moved to ease some local measures in time for Australia Day.

The cap on private gatherings will rise from 50 to 200 but groups over 50 will need to have a COVID-safe plan, appoint a COVID marshall, keep a guest list and use a QR code.

A density requirement of only one person to every two square metres will also remain with the change to take effect from Friday.

But the restrictions with NSW, which prevent people from Greater Sydney, the Central Coast and Wollongong from entering the state, will continue.

Premier Steven Marshall says this is in response to the six cases identified there last weekend.

But he says all being well, those measures will be lifted from January 31.

Chief Public Health Officer Nicola Spurrier said the changes on home gatherings would allow for some larger events, such as weddings, on private property.

"We still want to have some safety around that, so that's the reason for the QR readers," she said.

"We'd also like a COVID marshall to be there."

Professor Spurrier said the remaining concerns with Sydney related to the movement of people around the metropolitan area.

She said there were also concerns surrounding the low testing rates in NSW.

"We'd like to see those testing numbers up to provide a bit more reassurance," she said.

"I do think we need to give this a little bit longer."

Police Commissioner Grant Stevens said SA was taking a conservative position with NSW partly because of the more relaxed restrictions within South Australia.

"We are allowing so many more things to happen in South Australia which means the risk for us, if someone does bring the virus in, is so much greater," he said.

"So we're taking a more measured approach to when we remove those restrictions for NSW."

SA reported two new virus cases on Thursday but they are considered old infections contracted overseas.

They remain in hotel quarantine after recently returning to Australia.

They are not linked to the group of tennis players and their supporters in Adelaide for an exhibition tournament later this month.

SA still has five active infections, all in hotel quarantine.

Professor Spurrier said no problems had been reported with the tennis group, who continued to be allowed out to train under strict supervision.