The Westpac Rescue Helicopter has joined the search for a trail runner that went missing in the Rimutaka Forest yesterday.

29-year-old Susan O'Brien has spent a night in the bush after going missing during the 20 kilometre XTERRA trail run in Wainuiomata.

Police Senior Sergeant James McKay says searchers were in the bush until 1.30 this morning, and three teams camped out for the night.

"They're flying the possible routes the runner took," he said. "They're using heat detection equipment to hopefully pick her up."

Three more search and rescue teams are being brought in.