One of the five is a close contact of a French backpacker who tested positive on Thursday, and four are casual contacts from an event at Perth Mess Hall in Northbridge on Sunday.

Given the infections among casual contacts, Premier Mark McGowan revealed that 400 people who attended the event would need to test and isolate for 14 days from exposure.

It means the group - including 100 people from a Fremantle backpackers - will be in quarantine until January 3.

Two of the five new cases are vaccinated, two are not and the vaccination status of the other is unclear, Mr McGowan said on Friday.

The fifth case was revealed midway through his morning press conference.

Mr McGowan confirmed the initial positive case, an unvaccinated French backpacker, had arrived in Australia in January 2020 - before the pandemic.

He travelled from Queensland to Perth on December 12, a day before travel restrictions between the two states were tightened.

The man felt unwell on Sunday but didn't get tested until Wednesday.

He is believed to have been infectious for almost a week, unwittingly attending more than a dozen venues across Perth during that time.

It's suspected he has the Delta variant - which was the predominant strain in Queensland when he travelled - but genomic sequencing is still underway to confirm if it might be the newer Omicron variant.

Nine of his 21 close contacts have tested negative, including the man's partner and housemates who are all vaccinated and have been moved to hotel quarantine.

There are 991 casual contacts, with 336 so far testing negative.

Mr McGowan expects there will be further community transmission, but has further locked down the state over "worrying" numbers interstate.

From Saturday, Queensland and South Australia will be upgraded to high risk states with further bans on who can travel.

There's questions too about the looming February 5 reopening.

"If we have community spread of the virus we'll have to consider what we do," Mr McGowan said.

"It may well come forward because if we have community spread of the virus ... it may well be that February 5 becomes redundant."

Residents of Perth and the Peel region were ordered to wear masks at all public indoor venues under an edict that came into effect from 6pm on Thursday.

It will remain until at least December 28 and also applies to people in other parts of the state who have been in Perth or Peel since December 16.

High-risk large public events including music festivals are cancelled during this time and all nightclubs closed.

The mask-wearing rule does not apply to home settings including family Christmas Day gatherings or during vigorous outdoor exercise.

Australian Associated Press