Some regions of Western Australia are going into a full lockdown after a hotel quarantine worker tested positive for COVID-19.

Areas including the Perth metropolitan area, the Peel region, and the south-west region will go into lockdown from 6pm (local time) on Sunday. This lockdown will last until 6pm on Friday.

WA Premier Mark McGowan says there were four active cases in quarantine at Sheraton Four Points in Perth where the security guard worked. Of these four cases, at least three are confirmed to be variant strains - two UK and one South Africa.

The worker tested positive on Saturday night. He last tested negative for COVID-19 on January 23.

"We are told the guard was working on the same floor as a positive UK variant case. The guard completed two 12-hour shifts on both January 26 and 27," he says.

How the security guard, who is in his 20s, became infected is still under investigation.

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"He developed symptoms on January 28, and phoned in sick and did not go to work at the quarantine facility."

McGowan says following discussions with the Chief Health Officer and Police Commissioner, several measures will be put in place during the lockdown:

• people in the Perth metropolitan area, the Peel region, and the south-west region are required to stay at home unless they are shopping for essentials, like groceries and medicine, seeking medical or health care they need, or looking after vulnerable people
• exercise within your neighbourhood is only allowed with one other person for one hour each day
• if you can't work from home or remotely, then you can go into work
• if you leave home for any reason, people must wear a mask at all times outside. If people need to do work indoors, then wearing a mask is also required
• there is also a requirement to wear masks on public transport.

"Do not travel further outside of this area until the lockdown is over. If you do need to travel outside the region, that can only occur if you need to return to your place of residence," McGowan says.

"The transport of essential goods into this region is permitted under our existing transport guidelines."

Several businesses, locations, and venues must close as a result of the lockdown. This includes:

• pubs, bars, and clubs
• gyms and indoor sport venues
• outdoor recreational facilities, including skate parks and playgrounds
• cinemas, casinos, and other entertainment venues
• places of worship
• libraries
• restaurants and cafes must close, but can provide a takeaway service.

Schools are also not allowed to start back for the year on Monday.

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There are also restrictions on movement. Among the regulations, people cannot visit each other's homes unless they're caring for someone vulnerable or in an emergency and cannot visit patients in hospitals or disability facilities unless there are exceptional circumstances. Weddings are also cancelled for the next five days and up to 10 people can attend funerals.

WA Health Minister Roger Cook says they know the infected security guard didn't go into a room at the quarantine facility and he "did not expose himself unnecessarily".

"Over the coming 24-48 hours we will be undertaking extensive contact tracing and our contact tracing teams were stood up early this morning and they are working hard," he says.

"This is obviously a very fresh situation and we are trying to get to the bottom of it."

So far, the people living with the security guard have returned a negative COVID-19 test result, "so that is a sign that we have really got on top of this quite early in terms of the incident".

McGowan is recommending states stop travel to Western Australia, and he says he's been in contact with Australian Prime Minister Scott Morrison and other colleagues to tell them about the situation.

"I have recommended that they put a stop to any travel into Western Australia as an extra precautionary measure," he says.

"Border controls are important here. And I 100 percent support them to ensure that we can get through this."

He adds this is an "extremely fast-moving situation", so he's convened a meeting of the state disaster council to ensure they're all working together.

"I know for many Western Australians, this is going to come as a shock. Western Australians have done so well for so long, but this week it is absolutely crucial that we stay home, maintain physical distancing, and personal hygiene, and get tested if you have symptoms."