Western Australia will halve isolation periods for COVID-infected people and their close contacts from Tuesday amid a growing Omicron outbreak.
The move to seven-day quarantine comes after WA recorded 26 new local cases on Monday, including some who were infectious while in the community.
Premier Mark McGowan had faced growing pressure to ease the 14-day quarantine requirement after eight schools were exposed to the virus in the first week of term, plunging hundreds of students and teachers into isolation.
The virus has also spread to the Pilbara mining sector, with some workers forced to spend two weeks isolating in accommodation villages.
Under revised definitions, close contacts will include household members, intimate partners or anyone who has had 15 minutes of face-to-face contact or spent two hours in a room with an infectious case while unmasked.
People will be able to leave self-quarantine after seven days if they return a negative rapid antigen test result.
Casual contacts will no longer have to isolate, but reporting positive RAT results to WA Health will become mandatory.
Mr McGowan said anyone currently in self-quarantine, including about 12,000 people who arrived over the weekend under a softening of hard border rules, will be able to leave on day seven upon returning a negative test.
WA will double its arrival cap to allow 530 international travellers per week.
"Western Australia is about to embark on its most challenging phase of the pandemic," the premier told reporters.
"Our safe and cautious approach throughout the pandemic has helped put WA in the best possible position to manage COVID-19 safely.
"But with more cases, the road ahead is about to get bumpy."
Mr McGowan had last month said close contact changes would only come into effect once "high daily caseloads" were recorded in the WA community.
He insisted on Monday he had not bowed to pressure from industry groups and the Australian Medical Association to fast-track the changes, saying the decision was based on health advice.
The premier also insisted a new date for the borders fully reopening had not been set as the state's third-dose vaccination rate climbed to 44 per cent.
WA's new definitions are stricter than those set by national cabinet and adopted by most other jurisdictions. They are broadly aligned with those of South Australia, where close contacts are required to isolate for 10 days rather than seven.
Different rules will apply to schools under the higher caseload setting, with the government determined to keep classrooms open.
Teachers and students who come into contact with a positive case but do not develop symptoms themselves will be encouraged to continue attending school, unless they had close one-on-one contact with the infected person.
Staff in those circumstances will be asked to take daily rapid antigen tests and quarantine when not at work.
