The Dawn Princess in Akaroa, New Zealand. Photo: Princess Cruises

Almost 200 cruise ship passengers who left Melbourne for a tour of New Zealand have been confined to their cabins after coming down with a stomach bug.

Norovirus has broken out aboard the Dawn Princess, which is carrying 1500 passengers as part of a 13-day trip around New Zealand, the Canterbury District Health Board has confirmed.

The Dawn Princess, which has about 1500 passengers on board, was in Akaroa on Saturday, Dunedin on Sunday and is expected to visit Fiordland on Monday.

It left Melbourne on November 28 and is due to return on Thursday. 

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Cruise operators Carnival Australia informed New Zealand health authorities of the outbreak.

Canterbury District Health Board medical officer of health Daniel Williams said passengers needed to be isolated for 24 hours after symptoms had settled. The symptoms took about one to three days to pass.

"We were told by the ship's doctor that the number of new cases were slowing down, but there were still new cases," Williams said.

"It is very easily spread from person to person and it can be quite difficult to contain when people are living close together. The best way to stop this sort of bug from spreading is to stay away from people until the symptoms have settled."

Williams said people who were or had been ill were not allowed off the ship when it docked.

Carnival Australia corporate communications manager David Jones said the situation had improved since the outbreak started and fewer passengers were now confined to their cabins.

He said "stringent sanitation" had been implemented on board.

Railings, door handles and lift buttons were being disinfected, self-service food areas had been closed and passengers isolated.

What is novirus?

The Ministry of Health's website states norovirus is highly infectious and spread easily from person to person. 

The virus could survive on contaminated surfaces even after cleaning with some disinfectants.

Those with norovirus were infectious for at least three days after their symptoms stopped and could be infectious for up to two weeks on some occasions.

Norovirus could be spread through contaminated food or drinks, touching contaminated surfaces or objects then putting your fingers in your mouth, having direct contact with an infected person (such as sharing food or eating from the same plate or cutlery), and through the air (when vomiting sent tiny particles into the air). 

Norovirus was also responsible for 169 outbreaks of illness in 2013, affecting 3685 people.

- The Press and AAP