"The person was wearing a surgical mask," Chant said.

"The individual was screened on arriving in Ballina airport and as I said, since arriving, they (have been) in the 14-day self-isolation. Any potential close contacts are being followed up."

Chant said the three locally acquired cases, which didn't appear to be linked to the Crossroads Hotel, were also based in southwestern Sydney.

Contact tracing experts are now working to determine how they became infected.

"We're not yet sure where they are linked to but we will re-interview people multiple times," Chant said.

Victoria recorded more than 300 cases of Covid-19 today, the state's highest total.

Chant said she was concerned about what's happening in the southern state but said it was up to NSW to "mop up any seeding".

"We can't become complacent about it, but we need to be optimistic and work together. We are as good as each individual part," she said.

The news comes as The Australian reported the state government was moving toward tightening Covid-19 restrictions further to restrict further potential outbreaks.

It is understood senior government ministers met on Wednesday evening to discuss making changes to existing public health orders, which are likely to target restaurants and cafes.

This in on top of new restrictions which include dropping individual booking numbers from 20 to 10.

There will also be a cap of 300 for venues and every patron will be made to register their details with the establishment. Previously, this was only mandatory for the person doing the booking.

Dedicated hygiene marshalls will also be employed at venues across the state to ensure they are following government policy and people are social distancing.

Chant said NSW was at a "critical phase" and the community and businesses needed to work together.

"People think their social groups won't infect them but the data tells differently," she said.