Police said two men in their 50s left a house on State Highway 12 at Omanaia, 30km west of Kaikohe, just before 10pm on Saturday, and tried to cross a ford which usually allowed access across a creek between the house and road.
Serious crash investigator Senior Constable Warren Bunn said as the men went to cross the ford, their van was swept more than 100m downstream.
The driver managed to escape the vehicle with minor injuries. The passenger, from Omanaia, was found dead on the bank a short way from the van.
"The ford itself is easily passable but with the heavy rain, the van has entered it and been swept away," Bunn said.
Volunteer fire crews from Rawene were also at the scene with the station's chief fire officer Dave Williams describing the downstream current as "pretty fierce" following heavy rain.
Williams said about 15 members of the man's family scoured the banks of the swollen waterway in driving rain and pitch darkness desperately trying to find him.
He was eventually found by one of the Rawene brigade's most experienced officers two hours later as he returned to parts of the stream that had previously been searched after noticing a slight kink in the water.
A rescue was mounted at midnight with the firefighter tied with ropes and held fast by emergency workers as he entered the raging torrent to pull the man free from under a branch.
Williams said family were relieved their loved one was found so quickly allaying fears he had been swept into the harbour.
Williams said he knew the deceased, "a really, really nice guy". "We're a small community, so [knowing the victim] is something we deal with regularly," Williams said.
Bunn said it was not yet clear whether the death would be classed as a fatal car crash or a drowning. If it was included as a fatality it would take the region's toll to 24. This compared with 2015's 23 road deaths in the region.
