The state is monitoring four active cases of the virus, the latest being a man in his 60s who is in hotel quarantine after returning from overseas.

Health Minister Roger Cook on Friday said the state's sewerage network would start being tested for COVID-19 within the next month.

"Western Australia is in a unique position to undertake work in this field, given our current state of no community transmission for the past five months," he said in a statement.

The testing aims to identify the existence of the virus to enable more targeted campaigns encouraging people to be tested.

Prime Minister Scott Morrison noted the news.

"I welcome the fact... that Western Australia is actually moving to sewage testing, which is an important other testing method to give us an understanding of the presence and the spread of the virus," he told reporters.

"This has also been done now in the ACT for some time and other jurisdictions."

The WA government on Friday also announced a $3 million fund to support the state's travel agents.

"The federal government's international border closures will continue to severely impact these businesses for some time to come," small business minister Paul Papalia said.

"Western Australia is the first and only state in the country to implement a dedicated travel agent support program of this kind."

Agents will be eligible for support packages of up to $10,000 under the scheme.

Australian Associated Press