Western Australia has detected one new local COVID-19 case linked to an infected French backpacker who travelled from Queensland.

Premier Mark McGowan has extended restrictions on gatherings and a mask mandate into the new year.

The new infection is a woman in her 20s, in quarantine since December 23, who was a close contact of an earlier case.

“This is good news and another encouraging result from this Delta outbreak,” Premier Mark McGowan told reporters on Monday.

More than 600 close contacts have been identified with 86 yet to be located and tested, 39 of whom attended a busy event at Perth Mess Hall in Northbridge eight days ago.

WA police were attempting to find the outstanding close contacts so they can be isolated.

“This is something that is worrying because we cannot be 100 per cent sure that the Delta virus is not lingering in the community,” Mr McGowan said.

Mr McGowan praised health workers at testing sites who have worked in scorching temperatures over the Christmas period.

He said their efforts, coupled with health restrictions limiting gatherings and a mask mandate, had yielded an “incredible” result with so few cases recorded.

“Given the high-risk nature of some of the exposure sites, we were expecting to see large numbers of positive cases,” he said.

“But so far, we have limited the spread and now are in reach of possibly being able to kill off this outbreak.”

However, Mr McGowan said WA remained at risk and the health restrictions would be extended to 6am on January 4.

“This gives us the best chance to potentially eliminate this outbreak in our community and ensure we can continue to have a relatively normal and safe holiday period,” he said.

The new case brings the total number of locally acquired infections in the current outbreak to nine.

The 25-year-old index case — an unvaccinated backpacker — visited nightclubs, shopping centres, restaurants and a cinema across multiple Perth suburbs after arriving in WA on December 12.

– AAP