A young woman and a firefighter were swept up to 30 metres down North Canterbury's Ashley River overnight, after four people were stranded on the roof of a 4WD.
The Fire Service said the water was up to the windows of the vehicle and rising when crews arrived at the scene in Rangiora.
Rangiora chief fire officer Hamish Peter said a firefighter who crossed the river while trying to rescue the woman lost his footing in the swift current.
He said the pair were grabbed by another firefighter downstream.
Mr Peter said he understands the group was off-road driving and became stuck in the river.
Police charged the 22-year-old driver with driving over the alcohol limit.
Ropes were used to bring the group safely to shore.