It's not exactly a visa extension but it's helpful to travellers who may find themselves stuck in Australia without a valid visa.
In the beginning of April 2020, the Australian government issued a new visa under subclass 408 specifically to visa holders affected by COVID-19.
It allows foreigners to remain in the country if they:
- have no other visa options;
- are unable to depart Australia due to COVID-19 travel restrictions; and
- remain in Australia to assist in critical sectors including healthcare, disability and aged care, childcare and agriculture during the COVID-19 pandemic.
The visa is free of charge to request.
Find more information and the application form here: https://immi.homeaffairs.gov.au/visas/getting-a-visa/visa-listing/temporary-activity-408/australian-government-endorsed-events