NSW Premier Gladys Berejiklian has urged tourism organisations in the state "not to interact" with Victorians crossing the border.
It comes with the news that extra COVID-19 testing clinics will open in Jindabyne and Cooma to tackle the risk of an outbreak as people flock to the mountains for a delayed start to the snow season.
"I call on all organisations not to interact with citizens from Melbourne at this stage, have activity elsewhere," Ms Berejiklian said.
"[Accommodation providers] are at liberty to accept or reject any traveller, but we are strongly, strongly sending out a message. Anyone who lives in those hotspots in Melbourne should not be moving around at all."
Victoria reported 17 new cases of coronavirus on Tuesday. Premier Daniel Andrews said he expected "significant community transmission" among that number.
Victoria has seen a spike in cases of community transmission over several days and six hotspots have been identified, in Brimbank, Cardinia, Casey, Darebin, Hume and Moreland.
NSW Deputy Premier John Barilaro said the Snowy Mountains were an area of "major concern" due to Victoria's rising caseload, with its school holidays just a week away.
"We know with school holidays, people may be heading to the ski fields for their winter recreation," he told 2GB on Tuesday.
"If Victorians are coming to the Snowy Mountains, you're not just risking the people living in Monaro.
"You're actually risking people living in Sydney, because there's going to be heaps of Sydneysiders up there this weekend skiing and then there could be an outbreak."
Mr Barilaro said extra COVID-19 testing clinics were open in Jindabyne and Cooma, with results to be returned within the hour for patients presenting at the Cooma clinic.
"We'll be able to pinpoint immediately if there is an issue," he said.
"We're putting all our measures in place, the resort owners are putting in place social distancing. In many cases they're only using 30 to 50 per cent of the resorts."
The ski season opened on Monday with limits of people using chairlifts and caps on patrons. Lift tickets must be pre-purchased so resorts can stick to strict limits.
Mr Barilaro said the government would "try to keep the borders open" but urged the community against interstate travel.
"Only travel if you need to. Don't travel across the border if you don't have to. Personal responsibility is at the heart of all of this."
Ian "Pom" Wheeldon runs four lodges across Thredbo and Jindabyne, and said he had already received several bookings for July.
"The reason [bookings] are okay for the school holidays is we slashed our prices in half because we assumed there was going to be limits to the number of people," he said.
He was concerned about a potential outbreak of COVID-19 but said no Victorians had booked one of his rooms, and they generally hit the slopes in their own state.
"We're worried, but we're also a business," he said.
"If you go back two and a half months, we'd written the season off. Now we're thinking we might turn over half of what we normally turn over."
In each of his facilities, Mr Wheeldon has closed off rooms that can be used by guests who are unwell.
ACT Chief Health Officer Kerryn Coleman has discouraged travel to the Victorian hotspots, but said it was unlikely travel restrictions would be imposed unless "things considerably change for the worse".