Britain will send four million Covid-19 vaccine doses to Australia, Prime Minister Scott Morrison announced Friday, as his country raced to halt a deadly virus outbreak.

The Australian leader said the planes delivering Pfizer vaccines were "on the tarmac" in the UK and would deliver "four million doses of hope" within weeks.

A first batch 292,000 doses will be shipped "shortly", the British government said in a separate statement.

Several of Australia's largest cities are in lockdown and case numbers and deaths are steadily rising, as the highly transmissible Delta variant spreads throughout the country.

Australia has a steady supply of the locally produced AstraZeneca vaccine, but residents have been hesitant to take it due to rare but highly publicised instances of the vaccine causing blood clots.

About 40 percent of Australian adults are fully vaccinated, well behind most rich nations, and the last 18 months have been marked by on-off restrictions.

Morrison said the vaccine delivery from "Downing Street to Down Under" was a "good deal between mates".

-Thanks Boris, I owe you a beer- Morrison said referring to his British counterpart, Prime Minister Boris Johnson.

As part of the swap deal, Australia will transfer four million Pfizer vaccine doses to the UK before the end of this year, the British government said.

Australia's most populous state of New South Wales reported 12 more deaths on Friday, with the daily toll expected to jump as more than a thousand people now contract the virus each day.