WA to reimpose 'hard' border with NSW

WA Premier Mark McGowan is reimposing the state's hard border for travellers from NSW. (AAP)

Western Australia is reinstating its hard border with New South Wales amid concerns the Sydney northern beaches outbreak is growing.

Premier Mark McGowan said WA's "low risk" rating for the eastern state had been upgraded to "medium risk", meaning that it would reinstate the same strict measures seen earlier in the year.

"This has been a difficult decision to make especially given the time of year," Mr McGowan said on Saturday.

"I understand this will be devastating news for people looking to meet family for Christmas in NSW."

But he said the alternative, if the virus comes into WA and causes a shutdown there over Christmas, would be worse.

"That's what we're trying to avoid here," he said.

Mr McGowan said WA's revised border measures had come following an Australian Health Protection Principal Committee meeting, where health chief across the country had received the latest advice.

The only people from NSW able to fly into WA after midnight on Saturday will be those with special exemptions.

Mr McGowan had a strong message for NSW contact tracers chasing down infections: "They need to get it under control".