New Zealand's borders will be closed to everyone but citizens and residents from tonight, Prime Minister Jacinda Ardern has announced.

Ardern said there were significant outbreaks in other countries, even though there was no evidence of community transmission in New Zealand.

All confirmed coronavirus cases in New Zealand related to overseas travel, she said.

"We need to continue to make further decisions and further restrictions."

From 11.59pm tonight, New Zealand borders will be closed to all non-residents and non-New Zealand citizens due to Covid-19 concerns, Ardern said.

New Zealand citizens and permanent residents will be able to return, and that includes the children and partners of citizens and permanent residents.

The first cases of Covid-19 in the Pacific mean that the changes also apply to the Pacific nations, which had previously been exempt to travel restrictions.

There would be exemptions, including for key health professionals, she said.

Ardern said she was increasingly concerned about international visitors refusing to self-isolate, and that has prompted these tough new measures.

She said the new measures would hurt the economy further, but health concerns were more important.

At no time in New Zealand's history has a power like this been used," she said, but health concerns and slowing the spread of Covid-19 was the most important task at the moment.

"That is how we help our jobs and economy too."

She said those who staffed services supporting freight, including by sea and air, would continue, meaning supermarkets would continue to be stocked.

She said the border restrictions would be reviewed on the same 16-day timetable as previously.

She said tourists in New Zealand already must abide by self-isolation requirements.

Tourists here in New Zealand for longer than 14 days already should check to see if they can leave the country.

The announcement follows a special meeting of Cabinet, held this afternoon and chaired by the Prime Minister, which included a discussion about whether travel restrictions to and from the Pacific needed to change following the first Covid-19 cases in Fiji and Samoa.

Cabinet had decided on the border shut down when it met at 4pm, and Ardern contacted her Australian counterpart Scott Morrison after the decision was made - but she said Morrison's decision to do the same in Australia had no influence on Ardern's decision.

"This decision was made between 4pm and 5pm this evening."

She did not notify any other world leader.

In comes just five days after the Government announced that every person from every country, excluding the Pacific Islands, would have to self-isolate for 14 days when coming to New Zealand.

"Alongside Israel and a small number of pacific islands who have effectively closed their borders this decision will mean New Zealand will have the widest ranging and toughest border restrictions of any country in the world," she said at the time.

Ardern's announcement comes just hours after Deputy Prime Minister Winston Peters told the House that the Government would give an answer to whether the borders will be shut to non-residents "very, very soon".