WA’s latest coronavirus patient attended a Perth concert alongside more than 1500 people while being tested for the deadly virus, it has been revealed.

The western suburbs woman, aged in her 70s, was today confirmed as WA’s fourth coronavirus diagnosis.

The woman had been in Cuba in recent weeks had flown from London to Perth on Qantas’ direct flight — QF 10 — on Thursday night.

The woman was tested for COVID-19 on Friday but didn’t wait for the results before attending a the West Australian Symphony Orchestra’s Absolute Beethoven concert on Saturday night.

It is unclear whether she was instructed to self-quarantine by medical professionals.

WA Chief Health Officer Andrew Robertson said people who had been in contact with the woman, including some of the more than 1500 people at the concert, were being tracked down.

"It was very regrettable she decided to do that and certainly we encourage people not to do that,” he said.

“We will be contact tracing all the people on the plane.”

It's not clear how far the Health Department will spread its net over the hundreds of people who were at WASO concert on Saturday night.

Health Minister Roger Cook said defended the woman, saying: “people make mistakes and that's ok we are working as a community together to try to resolve these issues to try to get on top of this bug”.

Of more than 16-hundred tests in WA, only four so far have been positive.

James Kwan died, after contracting the virus on board the Diamond Princess. His wife was today discharged from hospital.

WA's third case arrived from Iceland on an Emirates flight last week.

The source of their infections is a mystery along with how many others they may have exposed to it.

Meanwhile Premier Mark McGowan has blasted those who fought over toilet paper amid a supermarket shortage.

Coles has reduced it's cap for toilet paper to one park, sparking angry scenes in West Leederville and at Woolies in Innaloo dozens of shoppers waited for the roller doors to go up. The store limiting its customers to two packets per transaction.

“The images of people fighting over toilet paper is frankly disgraceful,” Mr McGowan said.