A rescue helicopter has winched a family, including children, to safety from the roof of their vehicle after it became trapped in the Waimakariri River last night.

Police told the Herald three people - a woman and two children - were saved in the dramatic incident about 40km north-west of Christchurch, but Garden City Helicopters general manager Simon Duncan said it was actually a family of five which were helped.

All were retrieved safely, Duncan said.

"They were okay, but cold ... they were [stuck in the river] 90 minutes all up."

The helicopter crew of three were too busy to speak to the Herald but had shared details of the rescue with their boss.

The family group told their rescuers they had become trapped about 6.30pm after they went to retrieve a jet boat which had become stuck, Duncan said.

Their 4WD vehicle then became stuck itself, prompting the call for help to the section of river near Eyrewell Forest.

Weather conditions were calm and dry, and the river flow wasn't high, but that didn't mean the rescue wasn't challenging for the crew of pilot George McInnes, crewman Wayne Ledgerwood and the paramedic, he said.

"Trying to extract five people when it's blowing 60 knots of wind [from the helicopter] isn't easy ... and it's cold and dark."

Night vision goggles were also used as all five were winched from the vehicle into the helicopter before they were flown to safety on the northern bank.

"They were quite relieved."

St John Ambulance couldn't be contacted tonight, but a police spokesman said earlier that although no one was injured the main concern was hypothermia, particularly among the three children involved.

Temperatures at the time the rescue unfolded were around 1C.

The spokesman also said before the helicopter rescue another vehicle had attempted to winch the stricken car to safety, but failed to gain enough traction in the difficult terrain.