Coronavirus: Premier Mark McGowan reveals border decision amid COVID-19 outbreak in Melbourne

All arrivals from Victoria will be required to self-quarantine until they return a negative COVID-19 test result.

Mark McGowan said the changes to WA’s border controls with Victoria would come into effect from 6pm tonight.

The new restrictions mean the Essendon Football Club will have to isolate on arrival in Perth on Thursday ahead their clash with West Coast.

But there’s no plans, at this stage, to slash the crowd capacity at Optus Stadium for Saturday’s match, the Premier said.

Anyone who has been to one of the exposure sites linked to the Melbourne cluster must self-quarantine for 14 days and be tested on day two and 11.

All arrivals from Victoria must wear a mask while travelling from Perth Airport to their accommodation or to be tested, and until they return a negative result.

They are also banned from using public transport until they test negative. Those arriving by road must also wear masks until they return a negative result.

Those who have arrived in WA from Victoria between May 15 and 6pm today will be contacted by WA Police via the G2G Pass system with advice about the exposure locations.

Anyone who is unwell or experiencing symptoms is being urged to get tested immediately, especially if they have recently been in Victoria.

Mr McGowan described it as a “very concerning situation”, with today’s positive cases meaning there have potentially been infectious people in the Victorian community since May 15.

“I will do whatever it takes to keep Western Australia safe and we won't hesitate to put in place additional border controls if that is what the health advice recommends,” he said.

On Tuesday, the cluster in Melbourne’s northern suburbs grew to nine cases, with four new infections detected in the community. They are all family contacts of the fifth case announced this morning.

The Department of Health in Victoria has identified 168 primary close contacts related to exposure sites. So far, 84 people have tested negative.

Victoria’s Chief Health Officer Brett Sutton said the nine cases were currently limited to three households, adding that private residences were often the most at-risk environments.