NSW residents were advised on Wednesday not to travel to SA while the border remained open, prompting the NSW opposition to call on the Premier Gladys Berejiklian to immediately shut it.

However, the nation's acting Chief Medical Officer Paul Kelly said there was no need for other states to close their borders.

"Essentially it is a moot point because with these new measures that come into force at midnight, all South Australians will be staying at home, they won't be going across any borders," he said.

SA Premier Steve Marshall announced his state would enter a six-day lockdown from midnight after a cluster of cases in Adelaide grew by two cases to 22.

Meanwhile, a croaky-voiced Ms Berejiklian said she had tested negative to coronavirus and was confident SA had the outbreak under control.

NSW Health said anyone who had recently returned from Adelaide and had been to any of the sites of concern listed on the SA Health website should get tested immediately.

Anyone who visited Adelaide on or since November 7 should minimise contact with other people until 14 days after the last day in that city.

"That means avoiding contact with other households, and minimising contact at work and socially as much as possible."

NSW Health was also contacting people who recently arrived on flights from SA, and screening all new arrivals who travelled via plane and bus.

NSW Health said there were seven COVID-19 cases in returned travellers in hotel quarantine in the 17,047 tests taken in the 24 hours to 8pm on Tuesday.

Australian Associated Press