Australians living overseas could be "trapped" in Australia if they return, after the nation's government tightened its border rules without notice.

Since March last year, the country has banned its citizens from leaving the country as part of its Covid strategy.

That restriction has not previously applied to Australians who usually live in other countries.

But they will now need to apply for an exemption for outbound travel - in line with rules for other Australians.

Australia's tough border rules have been controversial. Critics say this change - in effect from 11 August - will further punish families and deter citizens from returning.

The government said the measure aimed to reduce the risk of Covid cases entering the country, as it grapples with its worst outbreaks in a year.

Australia already has a weekly limit on incoming travellers and bans foreigners from entry unless they have an exemption. Its policies are among the strictest globally.

Last month, it halved the number of permitted arrivals due to Delta variant outbreaks.

Many Australians have expressed outrage at the latest move, branded by some as barbaric.

Alexandra Phelan, who lives in the US, tweeted she was "waking up to news that I'm effectively exiled from my country".

While the closed-border policy has been mostly supported in Australia, many have also criticised its impact on citizens.

The BBC has been told of cases in the past year where Australians have been unable to leave to care for sick or dying loved ones, or to retrieve their children from relatives.

Legal experts have questioned whether Australia's rules breach constitutional rights by effectively preventing some citizens from being able to return.

The government has said Australia will not re-open until at least 80% of its population is vaccinated, likely to be sometime next year. The current total is 19%.

More than half of Australia's 26 million people are currently in lockdown, due to Delta outbreaks in Sydney, Melbourne and Brisbane.

Sydney - the worst-hit city - has recorded over 4,300 cases in its outbreak.

On Friday, New South Wales state reported 291 new cases - its highest daily number in the pandemic so far.