"If it was absolutely safe then we wouldn't be making this comment ... having 6500, 9500 people up to I think it's about 15,000 people on one day might be a challenge, NSW Health Minister Brad Hazzard said.

"At this point all I can say to those people who might be planning to attend and to the organisers themselves, just be very aware of the messages that will come from the NSW government over the next 24 to 48 hours," he said.

"It's not an easy one."

Mr Hazzard spoke moments after NSW Premier Gladys Berejiklian introduced alerts for Byron, Ballina, Tweed and Lismore shires including imposing the four square metre rule and mandatory masks in retail settings for those areas.

Read more: Hen's party link to new COVID case in NSW

While NSW had no community transmission in the 24 hours to 8pm on Tuesday, a man in his 20s had since tested positive after coming into contact with the hen's party that included a Queensland nurse carrying the virus.

Patrons in the four council areas will be required to be seated in hotels, and residents within those local government areas have been urged not to leave the areas.

"We're not going to tell people to not go to that area for Easter ... but we ask everyone who was attending those areas over the long weekend to reconsider their plans," Ms Berejiklian said.

"There is no call for us to close borders, there is no call for us to go beyond what we are implementing."

The man in his 20s had "presented for testing and immediately did the right thing in terms of self-isolation", NSW chief medical officer Dr Kerry Chant said.

Venues where exposure may have occurred include the Henry Rous Tavern and Ballina Golf and Sports Club.

Patrons are advised to immediately self-isolate and get a test. A formal risk assessment is underway, Dr Chant said, while interviews with former cases have led to alerts for more venues.

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