New Zealand now has 14 new cases of Covid-19, taking the total number of cases to 53.

It is the largest rise in cases in a single day so far - and two of the cases have no link to overseas travel, meaning the risk of community transmission cannot be ruled out.

Director-General of Health Ashley Bloomfield has just made the announcement.

"We always knew that cases not linked to travel could happen and we are prepared for that," he said.

Another 1500 tests were processed in the last 24 hours, he said.

Of the confirmed cases, three people were in hospital and in a stable condition.

The new cases are in Auckland, Waikato, Taranaki, Manawatu, Taupo, Wellington, and Nelson.

Of the cases not linked to travel, one was in Auckland and one in Wairarapa.

Neither of the people had travelled overseas, so their relatives and friends' travel was being checked.

One of the people's partners had contact with people who travelled frequently.

The Ruby Princess cruise ship, which has just arrived in Sydney, had three confirmed Covid-19 cases, and 56 New Zealanders on board are being contacted. Of that total, 28 have already returned to New Zealand.

The update comes ahead of a State of the Nation speech by Prime Minister Jacinda Ardern, which will be broadcast from the Beehive at midday.

At last count, there were 39 positive tests of coronavirus in New Zealand.

There was no evidence of community transmission, though the Ministry of Health was still investigating the latest confirmed cases.

Speaking on Newshub Nation this morning, Director-General of Health Ashley Bloomfield said that if community transmission was confirmed, further measures would be introduced to encourage physical distancing.

That could include asking shops, bars and restaurants and close - as has been done in the UK and USA.

If an outbreak was localised, that specific region could be locked down with no travel allowed in or out. People who had left that area in the last few days would also be required to self-isolate.

"That could be a very effective way of not only stopping transmission in that community but preventing any onward transmission."

Existing measures like contact tracing, physical distancing, self-isolation and bans on large gatherings would also continue.

Some individuals and groups have been flouting bans on large gatherings. Earlier this week, Destiny Church said it would be going ahead with church services this weekend.

Bloomfield said the church would be rethinking that position.

"We also know that the Government does have powers to enforce the 100 maximum on gatherings. So if needs be, those powers will be used."

Education Minister Chris Hipkins said the decision to leave New Zealand schools open was based on the best medical advice, and the fact that there was no evidence of community transmission at this stage.

Plans were in place if spread in the community was confirmed. Those could include bringing school holidays forward and extending them.

The Government was also in talks with telecommunications companies about access to broadband for all students, and possibly removing data caps to allow digital learning in all homes.

Further measures to contain Covid-19 were announced yesterday, including temporary closure of libraries, art galleries, museums and university lecture theatres.

New Zealand closed its borders to non-residents and non-citizens on Friday, and other countries have gone into lockdown with citizens told to return home.

Italy, with 60 million citizens, has recorded 3405 deaths, exceeding the 3248 in China, a country with a population 20 times larger.

It took three months to reach 100,000 coronavirus cases worldwide. The second 100,000 took only 12 days.