Coronavirus: WA border closure in effect, residents who haven't returned could be denied entry

Western Australian residents who have not yet returned to the state now face being turned around in the toughest border control measures to be introduced in Australia.

Only health, emergency and other essential workers are now allowed entry into the state after the new measures aimed at preventing the spread of COVID-19 in the state came into effect from midnight.

It comes as 17 more West Australians were diagnosed with the new coronavirus overnight, including five cases where the source of the virus is still being investigated.

The new cases bring the state's total to 453, with 148 of those having recovered.

"The border closure will cause a great deal of frustration for many people. It will mean that some people's lives will be turned upside down," WA Premier Mark McGowan told a press conference this afternoon.

"But we are in a state of emergency. The situation we find ourselves in is not of our making, but we need to take extraordinary steps to protect our citizens.

"We make no apologies here. We need to use our isolation to our advantage."

Mr McGowan likened the closure to Brexit.

"Brexit has taken four years and we put borders in place in the space of one week," Mr McGowan told reporters.

Under the new measures, exemptions will be made for those working in the health and emergency services, defence, policing, mining industry workforces, flight crews and freight of essential goods, via ports and trucks.

Fly-in-fly-out workers will be permitted in but must undertake 14-day quarantines at the expense of their employers.

An exception will also be made for West Australians who have undergone 14-day quarantines in other states after returning from overseas.

However, these residents have only 24 hours to return to WA from the time they are released from quarantine and must still self-isolate for a further 14 days.

Exemptions may also be made on compassionate grounds.

Mr McGowan warned that anyone attempting to get around the border controls would be punished.

"Checks will be occurring," he said.

"If you have lied on an exemption form to get in to our state, there is every chance you will get caught and be forced to face the consequences."

Other new measures include a ban on travel to the holiday hotspot of Esperance on the state's south coast and the Kimberley, which is home to a high proportion of Indigenous Australians, who are at a heightened risk from COVID-19.