Australia and New Zealand started sealing off their borders Thursday, announcing unprecedented bans on entry for non-residents in a bid to stem the rise of COVID-19 infections.

Prime Minister Scott Morrison said the ban on anyone who is not a citizen or permanent resident coming to Australia "will be in place from 9:00 pm tomorrow evening".

A similar measure was announced by his New Zealand counterpart Jacinda Ardern, who acknowledged: "I recognise how extraordinary this is. In no time in New Zealand's history has a power like this been used."

Australia and New Zealand have announced a slew of restrictions to tackle the pandemic, but have so far stopped short of closing schools or instituting wider-ranging lockdowns.

Policymakers hope the bans will slow the rate of infection enough to avoid more draconian measures that would cripple the two economies and transform life for months to come.

Australia currently has 642 confirmed cases of coronavirus, with the total doubling roughly every three days. New Zealand has 28 cases.

Morrison said around 80 percent of Australia's coronavirus cases came from "someone who has contracted the virus overseas or someone who has had direct contact with someone who has returned from overseas".

A recent opinion poll showed 69 percent of Australians back closing the border.

Ardern said the measures would also ban visa holders.

"Today's decision stops any tourist, or temporary visa holder such as students or temporary workers, from coming to and entering into New Zealand."