Previously, only the organiser of a gathering was liable to receive a fine if the number of people at the premises breached the Public Health Order but, from Monday, every person in attendance will now be held individually responsible for the breach.

The total number of visitors includes adults and children but members of the household are not counted among the 20-visitor limit.

The NSW Government says the changes aim to ensure the safety of the community ahead of an expected increase in gatherings associated with Christmas and end-of-year festivities.

Operation Corona Virus Commander, Assistant Commissioner Tony Crandell, said the amendments had been made with community safety in mind.

"Coming into the warmer months, and with end-of-year festivities around the corner, it's only natural that people will have additional reasons to want to gather and get together," Assistant Commissioner Crandell said.

"These amendments aim to ensure that an increase in expected gatherings doesn't mean an increase in COVID-19 cases.

"The new changes come in addition to other restrictions which remain in place, including a limit on numbers at outdoor gatherings and licensed premises.

"NSW Police will continue to work with the community to ensure compliance to all restrictions under the Public Health Order.

"While the vast majority of people within NSW are doing their part, we will continue to target those who don't."

Other amendments have also come into effect that impact places of worship, auctions/open homes, weddings, and party buses.

More information here.