Six cases remain active in WA, where the interstate borders remain closed and there has been no confirmed community transmission since April 12.

About 50 Australian Defence Force reservists have been provided to help manage security at the hotels where returned overseas travellers are in quarantine.

About 240 security guards are stationed across the five hotels, supported by medical staff from the Department of Health.

Premier Mark McGowan says the evidence suggests WA's hotel quarantine system is working well.

"We have a very comprehensive arrangement in our hotels to make sure that we don't have any glitches or problems emerge from hotel quarantine," Mr McGowan said on Tuesday.

"But the ADF will help. They've done their initial training and they're on site now."

The McGowan government has resisted removing restrictions that were due to end last month, allowing 60,000 capacity crowds at Optus Stadium and the removal of the two square metre rule at pubs and other venues.

A decision is due later this week on whether to proceed with phase five from August 15, with a further delay likely.

South Australia this week brought back some restrictions as Victoria introduced the most severe lockdown the nation has seen during the pandemic.

Mr McGowan said he was comfortable with WA's existing arrangements but that could change if community spread returned.

"They've had some cases come into South Australia which I think has prompted that result," he said.

"We haven't had any cases come in, as far as we're aware. But obviously if cases do come back, if we have any community spread, we'll have to take actions to reduce the prospect of it spreading further."

Australian Associated Press