THE New South Wales Government has strongly encouraged residents to use masks if unable to social distance.

The advice from the NSW Chief Health Officer Dr Kerry Chant specifically recommends the use of face masks in indoor settings where physical distancing is hard to maintain, such as on public transport or in supermarkets,  in indoor settings with a higher risk of transmission, such as for the staff of hospitality and customer-facing venues and during attendance at places of worship.

Wearing a mask in any of these settings is not mandatory but is highly recommended, especially in areas where there has been community transmission.

Premier Gladys Berejiklian said a mask is not a substitute for physical distancing.

"People should continue to maintain their physical distance – it is our most effective weapon. However, if you find yourself in a situation where you can't maintain your physical distance you should wear a mask," Ms Berejiklian said.

"It is critical the community understands masks should be used in conjunction with other measures, and not as a standalone measure."

Masks should be considered a "fourth line of defence" after staying home if unwell and getting tested, maintaining 1.5-metre social distancing and good hand hygiene.

Dr Chant said masks are not suitable for everyone such as young children.

"Currently in NSW, the rate of community transmission does not call for mandatory mask use in the general population," Dr Chant said.

"However, along with practising good hand-hygiene, people are encouraged to wear face masks particularly in indoor settings where physical distancing is hard to maintain, such as on public transport. Most of all, stay home if you are unwell.

"NSW Health is continuing to monitor the situation and provide timely advice to the Government on the best defence against this once-in-a-100-year pandemic."

In Victoria the wearing of masks in public is mandatory from Monday, with regional Victoria to go into stage 3 restrictions from Wednesday night.