A long line of frustrated customers formed at Wellington Airport tonight, as customers tried to rebook their flights after planes were grounded.

The weather was "affecting flight systems", the airport said, and travellers were being urged to check the status of their flights online. Arriving flights were being diverted.

About 80 people were queued in front of the Air New Zealand desk. Many more were scattered around the airport on their phones, trying on organise a place to stay tonight.

Some were close to tears, while others were venting their frustration at airport staff.

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Max Allgrave said he and his girlfriend didn't know what to do.

"We don't want to stay here tonight. But we don't know anyone in the city, either.

"We're just hoping there's some hotel that can take us."

Alex Grey was in town for a conference, and now trapped in the city.

She said it was frustrating, as the weather had caused hours of delays before the cancellation was announced.

Customers were being told to rebook through their airline.

A statement from the airport said airways instruments were affected by the weather conditions just after 8pm.

"All flights were immediately diverted or cancelled. The Airways team are on site and investigating.

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"Around 10 domestic flights have been affected and international flights are not due to arrive until midnight," the airport said.

The airport said if the situation hadn't improved by midnight, international flights would also be diverted.

Wellington Airport seems to have improved its customer service from a week ago when flights were grounded because of fog.

This time around, music was turned down to allow travellers stuck overnight to try to get some sleep.

Blankets and pillows were handed out, while food outlets on the ground floor stayed open late.

Flight radars show some planes were being sent back to where they came from.

Air NZ flight 449 left Auckland at 7.14pm, headed all the way to Wellington, then turned around and flew back, arriving at Auckland again at 9.19pm, according to flight logs.

MetService meteorologist Brian Mercer said he couldn't be sure why flights were grounded but said visibility had been extremely low in the last hour or so due to a combination of low cloud and heavy rain.

"When it gets to a situation where it obscures visibility there are certain rules airports have to follow," he said. "For the past half hour there has been very, very reduced visibility."