More than 620 of the passengers on the Diamond Princess liner have been infected on the ship, which has been quarantined since February 3, initially with about 3,700 people on board.

The two passengers were an 87-year-old man who had suffered from heart ailments and bronchitis, and an 84-year-old woman.

Both tested positive for the virus although the woman's cause of death was listed as pneumonia, Japan's health ministry said.

It also said one health ministry official and another from the Cabinet Secretariat were confirmed to be infected with the virus after both had spent time working on the Diamond Princess.

Three officials had previously been infected.

The Australian government has said all Australians on the ship were stable.

Japanese media reported that 29 people were in serious condition, including one who had earlier tested negative for the virus, which the health ministry could not immediately confirm.

Japan has well over half the known cases outside China due to the ship infections and the rapid spread of the virus and the quarantine operation has sparked criticism of authorities just months before Tokyo is due to host the Summer Olympics.

Chief Cabinet Secretary Yoshihide Suga defended Japan's efforts. He told a news conference that after measures were put in place to isolate passengers on February 5, the number of new infections was now almost at zero.

In a move to reassure the public, the health ministry also issued a statement in both English and Japanese that said all passengers had been required to stay in their cabins since February 5 to contain the virus.

Criticism of the government has played out in social media as well as in parliament.

About 500 passengers began disembarking on Thursday while another 100 people were to leave for chartered flights home, a health ministry official said.

An initial batch of passengers who had tested negative and shown no symptoms left the vessel on Wednesday.

Those who have shared a room with people testing positive were required to remain in quarantine, as were crew. The ministry could not confirm how many people remained on board, or when disembarkation would be complete.

Some Hong Kong passengers went home, while Canadians were due to leave on a charter flight in the early hours of Friday, a Canadian government spokeswoman said. An evacuation flight was also being arranged for British nationals to leave Tokyo on Friday.

Earlier in the week, the United States evacuated more than 300 nationals on two chartered flights.

More than 150 Australian passengers arrived home after a pre-dawn departure from Tokyo's Haneda airport. They face another 14-day quarantine.

Disembarked Japanese passengers, however, face no such restrictions, a decision that has sparked concern.

Besides those on the cruise liner and returnees brought home from Wuhan in China, about 70 cases of domestic infections have been confirmed in Japan, including 25 in Tokyo, public broadcaster NHK reported.

Australian Associated Press