South Australia's new Premier has relaxed COVID close contact rules, as the state records 4,549 new cases and four COVID-linked deaths.

Quarantine for household close contacts has been reduced from 14 days to seven days, effective immediately.

"This is about bringing South Australia into line with the rest of the nation," Premier Peter Malinauskas said.

Mr Malinauskas also announced that as of 12:01am tomorrow, the definition of a close contact will change.

To be classed as a close contact, someone will have to have spent four hours in face-to-face unmasked interaction with a positive case. Previously the defined time period was just 15 minutes.

The government will also extend the time frame previously infected people are exempted from consideration as close contacts, from 8 weeks to 12.

The state's latest case numbers brings the total number of active cases to 28,198.

The four COVID-linked deaths include men in their 30s, 40s and 80s, and a woman in her 90s.

The state has 157 people with COVID-19 in hospital, including six in intensive care.

Mr Malinauskas also flagged that mask rules will be relaxed on April 14, unless significant changes occur.

However, people attending events at Adelaide Oval will now only need to wear masks when entering and exiting the oval, and in fully enclosed indoor areas.

"If you're at the footy and you're lining up for your chips and a Coke, or something else, then you will not have to wear a mask unless it's in a fully enclosed environment, which of course most places aren't at Adelaide Oval," Mr Malinauskas said.

Police Commissioner Grant Stevens will also seek a further 28-day extension of his powers under the Emergency Management Act, which was due to expire on April 1.

The rule changes come as Chief Public Health Officer Professor Nicola Spurrier said the state was facing a "BA.2 wave".

More to come.

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