Health officials in NSW are scrambling to figure out how three different people became infected with coronavirus as the state enters a “critical phase” of the pandemic.

Chief Health Officer Dr Kerry Chant announced 10 new cases of the virus, including three cases that were “under investigation”.

The three cases are not linked to the outbreak at the pub in Casula, which has since grown to 40 cases.

“There are three cases reported today under investigation and not currently linked to the Crossroads Hotel,” NSW Health said in a statement on Thursday afternoon.

“These include a female in her 40s from western Sydney, a female in her 40s from southwestern Sydney, and a man in his 30s from the Wollongong area.

“All three cases are currently isolating at home. Investigations to identify the source of infection and contact tracing are underway.”

Dr Chant said the aim of the department was “to find any crossover points with the list of venues” already identified in southwestern Sydney.

“Obviously we are concerned when we find cases that can’t be linked back because it does indicate we have missed a chain,” she said.

The Illawarra region has been separately linked to the Crossroads Hotel outbreak after the health department named a list of venues attended by cases traced back to the pub.

“Other venues attended by cases in the Crossroads Hotel cluster are under investigation,” NSW Health said.

These venues include Mancini’s Original Woodfire Pizza in Belfield, Hurricane’s Grill in Brighton-Le-Sands and Rashays in North Wollongong as well as Planet Fitness in Casula.

Dr Chant on Thursday said she could not “stress the criticality of the current time” enough.

“There have been several points where we’ve really needed the community and business and government to work together and this is probably one of them,” she told reporters.

“We’re clearly seeing high rates of testing, high rates of case numbers coming from Victoria but also we know that there’s a number of controls in Victoria now and it is important that we just mop up any seeding or mop up any transmission.

“I’m not complacent about the challenges of mopping up the transmission but I’m optimistic if we all work together, we can limit community transmission.

“But we are only as good as each individual part so it does require us to work together.”

She urged people to be mindful of their movements.

“Please just reflect, maintain that social distancing, don’t go out with your group of friends if you’ve got even the mildest of symptoms, don’t push through, stay home, get a test and really reflect on your activities over the next couple of weeks and really try and minimise your social interactions,” Dr Chant said.