Japan's Health Ministry says four Australians are among the 65 new confirmed cases of coronavirus on the Diamond Princess cruise ship, taking the total number of cases from the vessel to 135.

Key points: Authorities say they may test everyone onboard before allowing them to disembark

Authorities say they may test everyone onboard before allowing them to disembark There are 3,711 people on board, including 223 Australians

There are 3,711 people on board, including 223 Australians The ship was placed under quarantine on February 3 after a man tested positive

Health officials previously said 70 of the 3,711 passengers and crew on the Diamond Princess were infected.

Japanese authorities previously announced there had been 66 new cases, but the ship's captain corrected that number at 65 cases, including five crew members.

All passengers — including 223 Australians — are being quarantined on the vessel, docked at the port of Yokohama, south of Tokyo.

Japanese Health Minister Katsunobu Kato previously said the Government was considering testing everyone on board before allowing them to disembark.

Passengers have been voicing their concern about their wait on the ship, including by flying banners calling for help from the ship's balconies.

These passengers' banners read "Lack of medicine!" and "Thank you media". ( AP: Eugene Hoshiko )

Some Australians on board have told the ABC that conditions are "concerning", while others have said operators are "trying their best" in a tricky situation.

However, Mr Kato said his Government was "doing the utmost to keep everyone in good health".

Passengers taking it 'one day at a time'

Karen and Jason Honey, from Melbourne, during their hour of outdoor time. ( Supplied: Karen and Jason Honey )

The Diamond Princess was placed under quarantine after arriving at Yokohama on February 3, in the wake of a man who disembarked in Hong Kong being diagnosed with the virus.

Passengers have been allowed on decks in shifts in order to get fresh air and have been encouraged to regularly take their temperature.

The health ministry is separating its count of those on the ship who have been infected from those within Japan who have been infected.

The disease has killed more than 900 people, predominantly in mainland China, and infected more than 40,000.

Australian passengers Karen and Jason Honey from Melbourne told 7.30 they were "shaken" by news of the 65 new confirmed cases.

"But otherwise we are OK and are just trying to do one day at a time," Ms Honey said.

"We have been in isolation now for nearly six days," Mr Honey said.

"They are allowing us on deck one hour in every two to three days."

The Honeys said the staff on board had been doing their best under trying circumstances. ( Supplied: Karen and Jason Honey )

Ms Honey said the food they were being given was "not like what was on the ship beforehand, which is understandable".

"You can sort of probably put it between hospital and airline food," she told 7.30.

"We do feel that they are really trying their best. Princess have been fabulous. They are really — under the circumstances — they are trying their best."

Passengers have been allowed outside in shifts. ( AP via Kyodo News: Sadayuki Goto )

ABC/wires