People hoping to get domestic flights home on Air New Zealand this week are unsure if their flight will run and say they can't contact anyone to find out.

The deadline for domestic travel has been extended to Friday. Originally, it came into place at the same time as the level four coronavirus lockdown - Wednesday at 11.59pm.

But huge demand has meant that the government has pushed out the timeframe, transport minister Phil Twyford said. "The Government recognises New Zealanders are trying to do the right thing by returning home ahead of the country moving to level four."

After Friday, the only internal flights available will be for freight or people working in essential services. Overseas visitors and tourists will be able to use domestic air travel to get to an international airport to fly home. Others will not be able to fly.

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At a media briefing on Tuesday, Prime Minister Jacinda Ardern acknowledged getting people home via domestic ferries and flights had been "stressful" but asked for patience.

"We gave 48 hours to really start closing things down in terms of that unnecessary travel. But we accept, we've got to let people back to their place of residence. We'll work through that backlog so I do just ask for people's patience and to be calm."

Kevin Stent Thousands of worried domestic travellers are unsure whether they will be able to board their scheduled flights home as coronavirus shuts the country down.

Later on Tuesday, Twyford announced the deadline extension. Domestic passenger services, particularly ferries, had been inundated with people trying to get home before the cut-off date, he said.

A decrease in passenger numbers to accommodate physical distancing had reduced capacity and Twyford said it was unlikely the increased demand could be met before midnight Wednesday.

The government had "agreed to extend the deadline for non-essential workers and international tourists to keep using domestic passenger services until midnight Friday," he said.

"After this time, services will only be provided to essential services and workers, including freight services.

"International travellers will only be allowed to use domestic passenger services to reach their final destination to comply with lock-down requirements."

Tauranga couple Phil and Julie Pigneri travelled to Christchurch last week. Their scheduled flight home is on Thursday, but with no way of contacting Air New Zealand through Christchurch Airport or by phone or email, they have been unable to move their flight forward or find out if the flight will be running.

The couple went to Christchurch Airport to get answers on two separate occasions earlier this week and were met with a line of "about 1000 people" at the Air New Zealand terminal, Phil Pigneri said.

They hoped to move their flight forward to get home in time after Prime Minister Jacinda Ardern's announcement that all New Zealanders should return home as soon as possible and self-isolate.

"It was total waste of time, there's just too many people there and the lady at the desk even said there was nothing she could do and she didn't understand why so many people were lined up," Pigneri said.

"The frustrating thing is that Air New Zealand have a lot of planes...but from our viewpoint at the airport on two occasions, no planes were flying," he said.

Pigneri said they will return to the airport for their original Thursday flight, but have no idea what would happen in coming days.

"It's very frustrating that Air New Zealand got $900 million from the Government last week and can't do their job." he said, referring to the Government's loan to bail out the airline.

The Government is warning travellers not to go to airports unless they have a ticket. Instead, travellers should contact a travel agent or airline directly, or contact their country's embassy.

A spokesperson for Air New Zealand said the airline was increasing capacity on domestic services over the next two days to help people get home before the lockdown.

This includes a mix of extra flights and swapping smaller planes for larger ones. Details can be found on the Travel Alerts page on the Air new Zealand website.

"We are also working through what domestic and international flight schedules will look like when the country is at Alert Level 4 and will provide an update as soon as we are able to," the spokesperson said

The airline asks travellers cancelling a flight booked in the next 48 hours to inform them online so seats can be freed up for others, and tells those needing a credit or refund to call them only after March 31.

"We are wanting to ensure that our phone lines and social media channels are best placed to assist customers urgently needing to travel."