Authorities say international travellers are continuing to party in Sydney's youth hostels and are threatening to spread COVID-19 among themselves and the public.

A group of backpackers were spotted drinking on the rooftop of a Kings Cross hostel on Tuesday evening, prompting neighbours to tip off police who dispersed the crowd.

Mr Fuller urged others to do the same should they witness travellers disregarding strict rules which limit indoor and outdoor non-essential gatherings to two people.

"If you see people congregating, particularly drinking in the park or backpackers who are international travellers ... please report it and we will respond," he told reporters in Sydney on Thursday.

"The community are reporting people who are breaking these isolation laws.

"There's lots of people who do believe in isolation and do understand it."

A backpacker residence in Bondi has already closed its doors as it could no longer comply with the new restrictions, Mr Fuller added.

Sydney's east has become a focus for authorities, with a pop-up COVID-19 testing clinic set up in Bondi after virus clusters developed within the city's backpacker community.

NSW Health said more than 115 people were tested within the first few hours of the facility opening on Wednesday.

The Berejiklian government is advising backpackers to fly home, with NSW Attorney-General Mark Speakman saying now is not the time for sight-seeing.

"They've come to Australia for tourism," he told ABC TV on Wednesday afternoon.

"Tourism isn't a reasonable excuse. Working, learning, getting food, medical supplies and so on are reasonable excuses.

"It doesn't leave much else for backpackers to do and they should be going home."

Prime Minister Scott Morrison on Thursday told reporters that the federal government is looking at how backpackers who work in health, disability or aged care can be "better utilised" during the COVID-19 crisis in Australia.

Australian Associated Press