More power has been given to medical officers to stop the spread of coronavirus in New Zealand.

Prime Minister Jacinda Ardern announced new quarantine measures on Monday that give medical officers the ability to quarantine ships, aircraft and travellers coming into New Zealand if there are "grounds to believe there may be cases of COVID-19 on board".

She said there had been no need to use them so far, but they were there if required. These powers were given under the Health Act of 1956.

"This steps up powers from being able to quarantine individuals and extends it to an ability to quarantine entire vessels," she said at a post-Cabinet press conference.

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Ardern also announced an extension of the temporary travel restrictions, which are stopping people travelling from or transitting through various countries including mainland China. These restrictions would continue for another seven days.

She also provided an update on the New Zealanders abroad during the outbreak.

The Ministry of Foreign Affairs and Trade are monitoring the "handful of cruise ships and river boats" that have been quarantined and are carrying New Zealanders.

Earlier, the Ministry of Health director-general of health Dr Ashley Bloomfield said there were 13 Kiwis aboard the MSC Opera cruise ship off the coast of Greece.

CRUISE SHIP CASES

There were also eight passengers aboard the Diamond Princess ship, all of whom have been assessed. Five have passed the 14-day period of concern; one has been tested as negative, and another test is pending.

There were four New Zealanders currently on the Grand Princess off San Francisco. "We are not aware of any health concerns for any of those people," Bloomfield said on Monday.

"There is one New Zealander on [a Nile River cruise] that's quarantined also," he said. There were no concerns about this person.

Testing capacity is being lifted, he said, "We are able to process well over 1000 tests a day should that be required".

Passengers on the Grand Princess currently due to dock in Oakland will be required by US authorities to be quarantined, he said. The New Zealanders were staff aboard the ship, Bloomfield said.

"We're actively case finding now and we would be moving to do wider testing of probable cases. "We now have a growing number of countries overseas that are reporting an increasing number of cases," he said.

There's a cruise ship being held off Greece, there are 13 New Zealanders on board that, but the ministry is not aware of any health concerns, he said.

"It's still quite early in the development of that situation so we'll just keep a close eye on that," he said.

Bloomfield said the ministry was not aware of any health concerns for any of those passengers.

MEDICAL STAFF SELF-ISOLATE

Fifty-four hospital staff were asked to go into self-isolation after treating a "probable" case of coronavirus.

Bloomfield confirmed there are no new confirmed or probable cases of Covid-19 on Monday. The only person in New Zealand hospitalised by coronavirus would soon be discharged.

There had been 54 hospital staff asked to go into self-isolation after treating a probable case of Covid-19, he said. Some would be able to return to work on Wednesday.

Bloomfield said it was disappointing to hear lab workers were preparing a strike for this week. He said it was poor timing for a strike to be conducted.

There are currently five people who have been confirmed to have the illness in New Zealand. The number remains at five confirmed, and two probable cases.

GETTY New Zealand has five cases of Covid-19. In Italy, where cases are quickly rising, a man wears a face mask at Milan's city airport.

The first case, in Auckland Hospital, continues to improve. The hospital is planning this person's discharge currently, Bloomfield said.

Testing capacity is being lifted, he said, "We are able to process well over 1000 tests a day should that be required".

OTHER DEVELOPMENTS

Drive-through clinics for testing for the illness is an option on the table, he said.

"We're calling them community based assessment centres."

Bloomfield said the way the virus travels between people mean there is a window between close contacts receiving the virus and when they're infectious -- allowing health authorities to reach the person and "stomp out" the virus. Intense work was underway to track close contacts, he said.

He said they have actively looked at bringing back recent retirees from hospitals to raise staffing numbers if the situation gets worse.

As influenza season hits, Covid-19 will be added to regular swabbing of patients at "sentinel" general health practitioners, who report to the Ministry of Health about how the flu is spreading, Bloomfield said.

MONIQUE FORD / STUFF The Ministry of Health's Director-General of Health Dr Ashley Bloomfield delivering an update to the media on the response to Covid-19 coronavirus.

No new cases were reported on Sunday either. So far 224 tests have been completed with five returning a positive result.

Italy now has more positive cases of coronavirus than anywhere but China, with 7,375 infections with at least 366 deaths and 16 million people have been put into lockdown there. Ardern said there are currently 19 New Zealanders in Milan, Italy.

The World Health Organisation has provided new details on how the virus spreads, suggesting it is less contagious than influenza but can cause a more severe illness the the seasonal flu. Transmission does not appear to be driven by people who do not have symptoms.

The government on Monday also finalised the next steps in its plan to support businesses and workers hard hit by coronavirus.

Ardern announced a package to protect the economy that included wage subsidies.

WHAT YOU NEED TO KNOW

Covid-19 is a respiratory disease caused by a recently discovered new coronavirus. It spreads via droplets from the nose or mouth expelled when a person with the disease coughs, sneezes or exhales. To avoid infection, people should stay at least a metre away from someone who has, or may have, the virus.

Transmission does not appear to be driven by people who do not have symptoms.

The viral incubation period, that is time between catching the virus and showing symptoms, ranges between 1-14 days.

AP Students in the US wear face mask as they walking onto the University of Washington.

The most common symptoms are fever, tiredness and dry cough. Some patients may have aches and pains, nasal congestion, runny nose, sore throat or diarrhoea. Some people become infected but don't develop symptoms or become unwell.

From what we know thus far, about four in five people recover without needing special treatment. About one in six become seriously ill and develop difficulty breathing. About one in 50 die.

The risk of catching Covid-19 from someone with no symptoms is very low, because the virus spreads via droplets expelled by coughing. However, it is possible to catch the disease from someone with very mild symptoms, including a cough.

To minimise the spread of infection, wash your hands thoroughly with an alcohol-based rub or soap and water, cover your mouth and nose when coughing and sneezing, and keep at least a metre away from other people coughing and sneezing.

People who have been in or transited through China, Iran, northern Italy or the Republic of Korea, or have been in close contact with someone with Covid-19, should self-isolate for 14 days from the date of departure or close contact. They should also register with Healthline (0800 358 5453).

People who display symptoms should phone Healthline in the first instance – don't head straight to your doctor or medical centre.​

READ MORE:

* Coronavirus death toll estimated to reach 3,900 by Friday, according to AI modelling

* Govt to announce more economic help for businesses and workers

* Italy death toll goes from 233 to 366 deaths in a day

* From mild to fatal: how the coronavirus affects those who catch it

* 'Outbreak' or 'pandemic'? Translating coronavirus jargon

* NZ must ramp up containment, professor says​

​* Coronavirus: Full coverage