The scheduled departure of more than 400 passengers from the Diamond Princess on Friday after weeks in quarantine comes as the US Centers for Disease Control issued a low-level travel advisory for Japan.

Meanwhile some public gatherings in the country are being scrapped in a bid to contain the virus, which has killed more than 2200 people in mainland China so far.

More than 600 travellers aboard the liner, quarantined off Yokohama since arriving on February 3 with 3700 people aboard, have been infected with the virus. Two of them - both Japanese in their 80s - died on Thursday, and some 80 people around Japan, including 25 in the capital of Tokyo, have tested positive for the virus.

While foreign travellers leaving the ship face more quarantine at home, Japanese do not - a situation that has stoked concerns about Japan's quarantine practices.

A number of countries have flown nationals who were aboard the liner home: Two of the evacuated 170 Australians tested positive for the virus after they arrived in Darwin, Australian authorities said on Friday.

At a briefing on Friday, Chief cabinet secretary Yoshihide Suga defended the government's handling of those aboard the cruise ship as appropriate. More than 1000 passengers and crew will remain aboard after Friday.

'Many Japanese on social media expressed concern about their government's handling of the situation.

"There are still crew testing positive on the ship, yet people are being allowed to disembark - and told it's okay to use public transportation to get home, then told by the health ministry to avoid using public transportation after they are home," wrote one Twitter user using the handle 'Homo Sapiens'.

Australian Associated Press