New Zealanders overseas are being urged to come home, while commercial travel options are still available.

More than 80,000 Kiwis could be left stranded if they don't come home now, Foreign Affairs Minister Winston Peters says.

New Zealanders overseas are being urged to return home immediately as commercial flights begin to dry up, but some are already struggling to follow that advice.

As countries move to ramp up their travel restrictions, it's leading to a "reduction in passenger numbers and many air routes will not remain commercially viable for long," Mfat says.

ROSS GIBLIN/STUFF Foreign Affairs Minister Winston Peters, front left, and Prime Minister Jacinda Ardern are urging New Zealanders overseas to head home.

With worldwide flight schedules being slashed and a growing number of international borders being closed, the Ministry of Foreign Affairs and Trade (Mfat) issued the return home alert on Wednesday, as the coronavirus pandemic continued.

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Peters said there were about 17,000 registered travellers and others who were making contact now, he said.

STUFF Commercial flights into New Zealand may soon dry up, prompting our government to urge Kiwis abroad to come home now. (File photo)

"We are dealing with the global figure of 80,000 travelling; as for how many will respond, we don't know."

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Some at-risk Mfat staff were also being called home, he said.

SIMON LAIDLAW/SUPPLIED Christchurch man Simon Laidlaw says it is "total chaos" in the Philippines after the Government there declared a domestic travel ban by sea and air.

They had been asked if they wanted to return, while there were others where Mfat needed to act now, he said. "We are in serious consultation with them now."

Diplomatic staff were people in their own right with health issues in some cases, he said.

"It is wise for us to take precautions on what we know about their health rather than wait and find we could have acted but didn't."

The Ministry was being proactive, he said.

Meanwhile, he warned Kiwis travelling, "it's very likely you'll be cut off very shortly".

"If you can get home, start coming home now. We are alerting everyone that we can that transportation options are closing up real fast and they could be stranded there, so they need to think about it real hard now."

When asked if the Government would consider putting on flights if commercial airlines shut down, he said they were looking at the scale of what they have to deal with now. "But in terms of what you call Plan B, of course we are putting work into that."

"Put it this way, we are considering every option now."

The advice on the SafeTravel website was a significant escalation from previous advice, and followed official warnings for New Zealanders not to travel abroad "unless it is absolutely essential to do so".

But coming home is proving difficult for some.

Ian Phillips and his wife say they are stuck in Lima, Peru, after missing the New Zealand Government's tough border restrictions which came into force early Monday morning.

While the pair was registered on SafeTravel, they only received an alert on the updated travel advisory nine hours before the arrival deadline.

"Hardly enough time to arrange anything, and was some 19 hours after the announcement.

"It was only through the proactive action of our local tour company that managed to get use from Macchu Pichu to Lima where, at this point, we were unable to secure a flight," Phillips said.

Simon Laidlaw, from Lyttelton, previously told Stuff he was having trouble flying out of the Philippines. Since Mfat changed its travel advice, he says the situation has become quite stressful and turned into "total chaos".

"We got a message from our travel agent yesterday saying 'I think you have to get out of Cebu in 72 hours because of Singapore Airlines' new rules'.

"We are pretty stressed about it, we have been trying to get home nearly a week now."

Travelling New Zealanders were advised by Mfat to work with their travel agents and airlines to discuss options for returning home.

But Laidlaw says he's had to wait around five hours to speak to someone, and is now planning on travelling to Mactan-Cebu Airport to seek assistance.

All New Zealanders overseas will need to consider how best to keep themselves safe where they are "by following the advice of the World Health Organisation (WHO) and local health authorities", a MFAT spokesman said.

The agency is also encouraging all New Zealanders travelling or living overseas to register their details on the SafeTravel website.

Australian citizens abroad have also been told to come home by their federal government, with Australian Prime Minister Scott Morrison also moving to ban non-essential gatherings of 100 or more people indoors.

Air New Zealand is among the carriers bearing the brunt of heavy global travel restrictions, with thousands of job losses expected.

The airline will reduce its long-haul capacity by 85 per cent in the coming months and will operate a minimal schedule to allow Kiwis to return home and keep trade corridors open.

Prime Minister Jacinda Ardern announced on Saturday all people entering New Zealand, including citizens and returning residents, need to self-isolate for 14 days from Monday morning.

But the advice has now been expanded to include all people who have been out of the country in the past two weeks to enter self-isolation, reflecting the shifting goalposts agencies are facing in responding to the crisis.

"If you arrived before those border restrictions, seeing out the balance of your 14 days [in] self-isolation is sensible, safest and the best thing you can do for the community around you.

"We need New Zealanders to prepare. Think about Covid-19 the same way you would a civil defence emergency ... it is not a time for panic, it is a time for preparation," Ardern said.

There were 20 confirmed cases of Covid-19 in New Zealand as of Wednesday afternoon, as measures to prevent community spread ramp up.

Globally, there have been 184,976 cases and 7529 deaths across 159 countries, WHO says.