A 27-year-old man survived for six days on only rainwater while pinned tightly inside his crashed pick-up truck beneath a highway bridge in north-west Indiana, US police say.

His ordeal ended when two men scouting for fishing spots on Tuesday afternoon (local time) noticed the badly damaged vehicle, its white airbag deployed, and reached inside.

“They touched the body and the person turned their head and started talking to them. So, that got a little rise out of them,” Glen Fifield of the Indiana State Police told local news outlets.

The truck went off Interstate 94 ahead of a bridge over Salt Creek, missing the guardrail and likely rolling several times before landing on the other side of the creek, hidden out of sight from the road above, Fifield said.

Matthew R Reum of Mishawaka, Indiana, was freed from the wreckage on Tuesday night by first responders working under bright floodlights, then flown to hospital in South Bend with life-threatening injuries, Fifield said.

“He made it through the night. He is alive,” Fifield told the Associated Press.

Reum remained in a critical condition early on Wednesday.

Mario Garcia, one of the fishermen who found the wreck, said Reum was awake and “very happy to see us” after being exposed to the elements since December 20.

“It almost killed me there, because it was so shocking” to find him alive, Garcia said during a news conference in the nearby city of Portage, The Times of North-west Indiana reported.

Garcia, of Hobart, said Reum told them he had screamed and yelled for help, but heard only the “quiet sound of water”.

Reum told them his mobile phone had fallen out of reach and his body was trapped, preventing him from calling for aid.

Fifield said Reum had not been reported missing.

“Had it not been for the two individuals that were walking the creek this afternoon, this incident more than likely would have had a different outcome,” he said.

Reum’s “will to survive this crash was nothing short of extraordinary”.