Two Australian states have been put on alert overnight after officials confirmed new positive cases, with residents urged to check exposure sites.

Victoria posted an initial alert just before midnight, after a hotel quarantine worker at the Holiday Inn at Melbourne Airport tested positive to Covid-19 a day after returning to work and developing symptoms.

A "full public health response" is under way, with Holiday Inn Airport workers and others who are considered primary close contacts being contacted by Victoria's Department of Health.

Residents have been urged to check for exposure sites.

Earlier, NSW Health issued an alert for several venues after a returned traveller tested positive for Covid-19 two days after they were released from hotel quarantine.

Household contacts have tested negative and the results indicate the confirmed case has a low level of infection.

There are still new warnings for a number of venues in and around Wollongong and southern Sydney, including a hotel and cafe.

Other venues are listed as casual contacts, with attendees advised to get tested and self-isolate until they receive a negative result, and get tested again if they develop symptoms.

text by Natalie Brown and Bella Fowler, news.com.au