UPDATED 10.55am: The mum and her two sons, aged 10 and 12, who spent a wet night in the Tararua Ranges, are being treated for hypothermia.

They were airlifted out this morning, after being forced to hunker down for the night.

Rescue Coordination Centre spokesman Steve Rendle says two of the group are being treated for mild hypothermia and one has moderate symptoms.

The family had been walking on the Omega Track, in the mountains between the Wellington and Wairarapa regions, when they activated a personal locator beacon at 6.30pm yesterday.

The Rescue Coordination Centre (RCCNZ) was able to reach the mother on cellphone.

Rescuers learned the boys had become cold and exhausted on the walk from Kaitoke to Alpha Hut on what was intended to be a four-day tramp.

RCCNZ search and rescue mission coordinator John Ashby said strong winds and torrential rain in the area meant neither the Westpac Rescue helicopter, nor police land search and rescuers were able to reach the trio.

The family spent the night in cold and wet conditions but have now been rescued.

"They have had a cold wait in very uncomfortable, wet conditions but they had sufficient equipment for a four-day tramp and that has helped them get through the night," Ashby said.

"Without an emergency locator beacon to call for help, this would have been an extremely challenging situation for them."

They're being taken care of at the Trentham Army Base.