National cabinet has backed new international and domestic travel measures to strengthen COVID-19 protections in response to the growing threat of a highly infectious UK coronavirus variant.
Greater Brisbane has also been declared a coronavirus "hotspot" at the Commonwealth level, after a cleaner tested positive for the new variant - sending the city into a three-day lockdown.
Under the changes, passengers flying into Australia must return a negative COVID-19 test prior to departure and caps on returning travellers have also been reduced.
Passengers on flights from the United Kingdom will also be subject to rapid testing for the new variant of coronavirus before they board flights home.
Masks will be made mandatory on all domestic and international flights and at domestic airports in Australia - excluding children 12 and under - and recommended in overseas airports.
"This virus continues to write its own rules, and that means that we must continue to be adaptable in how we continue to fight it," Mr Morrison said.
There will be some exemptions to testing requirements, such as seasonal workers from low-risk countries where there is limited access to testing, who will instead be subject to "tailored" checks.
International arrival caps reduced until February
The caps on international arrivals returning to Australia have been reduced in New South Wales, Western Australia and Queensland by 50 per cent.
The revised cap in New South Wales will fall to 1,505 people per week, in Western Australia to 512 per week and in Queensland to 500 people per week.
Victoria will also continue to have a capacity of 490 people each week - after this was previously reduced following the state's second coronavirus wave.
National cabinet settled on the reduction until 15 February at the meeting of state and territory leaders on Friday.
Mr Morrison said 80 per cent of Australians registered overseas are now in countries where the new variant is evident.
"There are many unknowns and uncertainties in relation to the new strain, and so that's why this precautionary approach, we believe, is very sensible," he said.
Chief Medical Officer Paul Kelly said the "hard and fast and strong" response was aimed at heading off the risks posed by the new highly transmissible coronavirus.
"Our main issue is to keep Australians safe and to really make sure that this particular strain is not the one that becomes circulating in Australia," he said.
"The reason is because it will be much more difficult to control."
All quarantine workers will now also be tested daily.
International air crew must undergo a COVID-19 test in Australia every seven days or on arrival and will need to quarantine in dedicated facilities between flights.
Around 38,000 people are currently registered with the Department of Foreign Affairs and Trade as wanting to return from overseas.