Two new cases of COVID-19 have been confirmed in South Australia, with health authorities issuing an emergency health alert.

One of the new cases has been identified as a close contact of another confirmed case linked to Roma Mitchell Secondary College and Thebarton Senior College in Adelaide. The total number of cases linked to the cluster now stands at four.

Authorities are working to determine if the other person is a case of community transmission.

An emergency health alert has been issued as a result of the new cases requiring anyone who visited three location in Adelaide's north to self-isolate immediately.

The three locations include a Fernwood Fitness gym in Salisbury Downs on Saturday August 1 between 6.00pm and 8.30pm, the Agha Juice House in Balir Athol on Friday July 31 between 5.00pm and 7.30pm and Najafi Carpet Gallery in Kilburn on Wednesday July 29 between 5.00pm and 8.00pm.

Anyone present at the listed locations is required to quarantine for 14 days and get tested for the virus even if they are not experiencing any symptoms.

Tough restrictions will be reintroduced for South Australians from tomorrow as the state attempts to squash any possibility of second wave.

In the state's fight against rising case numbers, the number of visitors allowed in households will be reduced from 50to ten.

Pubs, bars and restaurants will only be able to serve those who are seated.

Source: 9News