West Australian Premier Mark McGowan warns the state is heading into the coronavirus "storm", but he is encouraged by it only recording 17 new cases of COVID-19 on Sunday.
Mr McGowan has also compared Sunday night's hard closure of WA's borders to Brexit, even though the state will still be part of the Commonwealth.
"What we have done in less than a week took Britain four years to work through," he said.
"Brexit has taken four years and we put borders in place in the space of one week."
The Premier also officially announced a ban on travelling to the south coast town of Esperance, except for essential travel.
"Unfortunately for people in Kalgoorlie, the Esperance holiday won't be happening this holiday period," he said.
The 17 new COVID-19 cases are aged between 26 and 78 and take the state's total to 453.
But 148 of those people have now recovered, an increase of 56 since Saturday, meaning as of yesterday there were 302 active COVID-19 cases.
Of the 17 new cases, nine relate to overseas travel and three are from cruise ships, including the Ruby Princess.
Sixteen are in the metropolitan area and one is in the Great Southern region.
There are currently 56 confirmed coronavirus patients in hospital, including 18 in intensive care units.
"These types of numbers continue to be encouraging however, by no means can we get complacent," Mr McGowan said.
"We need to continue to follow the rules, listen to the advice and practice good social distancing.
"We're still heading into the storm, but not out of it. Our best weapon in this war is you. And by that, I mean keeping up the social distancing, the hygiene and where appropriate social isolation."
A plane carrying 159 West Australians who had been stuck overseas landed at Perth airport overnight, with the passengers going immediately into 14 days of quarantine at a hotel.
Border closure will turn 'lives upside down', Premier says
Mr McGowan said the overnight border closure was a historic date and an unprecedented step in the battle to minimise the spread of coronavirus in WA.
He acknowledged the border closure would cause a "great deal frustration to many people" and "turn people's lives upside down", but said it was an emergency and "we need to take extraordinary steps to protect our citizens".
"It's something I never thought I'd be doing as the Premier of Western Australia," he said.
"But I'm 100 per cent confident that this is the right approach. It is exactly what we need to do to protect ourselves and our loved ones from this virus."
He said people who were not inside WA should now not come unless they had an exemption.
There will be exemptions for people who work in health services, emergency services, transport freight and logistics, as well as those who have specialist skills not available in WA for industry and business continuity, who work in national and state security and government, and court and judicial services.
FIFO workers and their families will also be allowed in, but will be placed in 14-day quarantine, paid for by their employer, when they enter the state.
There will be further exemptions on compassionate grounds. Western Australians in quarantine in other states will be allowed to return if they do not show signs of the virus.
However, they must return within 24 hours of their quarantine ending, and will be quarantined for a further 24 hours upon their return.
Mr McGowan said the restriction on travel to Esperance was designed to stop a holiday "flood", particularly from Kalgoorlie, and was implemented at the request of the local shire.
Police Commissioner Chris Dawson has advised Mr McGowan there was no further evidence of coronavirus on the Artania cruise ship, which was docked at Fremantle.
Five decks have now been "deep cleaned", and the WA Government continues to pressure the Commonwealth to make the ship leave as soon as possible.
A total of 17,744 people have tested negative to the virus in WA, including 2,680 from non-metropolitan areas.
