Almost 40 flights were delayed and three others turned around when a power failure, triggered by a smoke alarm, affected air traffic control systems nation-wide earlier today.
Planes are able to fly again after the nation's air traffic radar system went into back-up mode, grounding flights across New Zealand.
Airways, which is responsible for controlling all air movements, said a fire alarm triggered the main radar facility to revert to back-up mode. While this grounded flights, Airways said just before 2.30pm that services were able to leave the tarmac.
In a media conference this afternoon, Airways chief executive Graeme Sumner said 36 flights were delayed and three others had to turn around and land again because of the power failure affecting air traffic control systems today.
A partial evacuation of its radar centre in Christchurch was sparked by the alarm, he said.
"There was some smoke emanating from the uninterruptible power system. The Fire Service was called."
It took 45 minutes to restore power.
He said the 36 flights were delayed by an average of 50 minutes and there would be "some flow-on delays as a result of that".
"I just want to apologise to both our clients and to the travelling public for any disruption that was caused today," he said.
"Naturally we regret that. But the safety of the travelling public is our primary concern and as a result we hope that people can understand that the actions we took today were necessary to ensure that took place."
In an earlier statement Airways said a fire alarm had gone off at the building where the radar is housed.
"At approximately 1.20pm this afternoon, the fire alarm went off at Airway's Christchurch Andy Herd Building, where Airways main radar facility is housed," it said in a statement this afternoon.
"The fire alarm was set off by smoke from one of our two Uninterrupted Power Supplies (UPS) which had failed. Therefore our radar and communications system reverted to back-up system mode.
"While Airways was able to continue to safely manage domestic airborne traffic, as the system was in back-up mode a conservative approach to managing New Zealand's airspace was taken, which included halting departures within New Zealand airspace.
"Our airborne international flights were unaffected as our main Oceanic control centre is independently managed from Auckland.
"By 2pm we had identified the cause of the issue and by 2.15pm our operations were running normally on mains power supply with back-up, and normal operations had resumed (domestic flights were departing once again)."
A passenger on an Air NZ flight said his plane was preparing to take off when it was stopped. Fliers were told the air traffic communications was "down for all of NZ".
GNZ volcanologist Geoff Kilgour said on Twitter that he was told the issue was a 'radar failure'.
Passengers at Wellington Airport were told that while some flights were landing, none were taking off.
Another flyer told the Herald he was waiting on the tarmac and was informed "radar is out over the whole country".
Someone else on a Jetstar flight in Wellington says he was told the same while waiting to take off.
Another person in Napier confirmed they were grounded but said airport staff had been very helpful.
Airways is responsible for controlling all air movements across 30 million square kilometres of airspace in New Zealand and over the Pacific, handling over 1 million air traffic movements a year.
The company's air traffic controllers work from a radar centre in Christchurch and more than 15 control towers nationwide.