Premier Mark McGowan said the lack of further infections was a good start in crushing the latest outbreak, "but there is still a long way to go".

The premier has also announced a return of a hard border closure with Queensland in response to further local cases there.

"These are challenging days for the country. The Delta variant is testing our systems and our community like never before," he said.

"I have faith, however, that we will crush this outbreak and save lives and jobs."

Perth's four-day lockdown was sparked after a second virus infection was revealed on Monday night, both linked to a woman who recently returned to WA from NSW.

A man in his 30s is thought to have contracted the virus at the Indian Ocean Brewery.

He dined at the brewery last Tuesday, eating at a different table to the woman who returned from Sydney and subsequently tested positive to the Delta strain of the virus.

Another woman, aged 32, also tested positive after coming into contact with the original case, most likely at a Perth gym.

Mr McGowan said it was sad that some businesses would suffer during the lockdown and the government was working on an assistance package, with details to be finalised over the coming days.

Police have established eight checkpoints around the lockdown zone and stopped 555 vehicles on Monday night with 38 turned around.

As part of the lockdown, face masks are mandatory outside the home and people are only allowed to leave for essential reasons, including shopping for groceries, health care, or one hour of exercise.

Venues closed across the city include casinos, nightclubs, entertainment venues, beauty and hair salons, swimming pools, recreation and fitness centres and places of worship.

Weddings are limited to five people and funerals to 10.

The premier said health authorities were continuing to check on close and casual contacts of the current cases and he expected the list of potential exposure sites to grow.

He said not since the early days of the pandemic had so much of the country been subject to virus restrictions.

"This is an incredibly concerning time," Mr McGowan said.

Australian Associated Press