Police are investigating a fiery crash which left one person dead.

Emergency services were called around 2.30am on Tuesday after a car and a heavy truck crashed on State Highway 1 north of Atiamuri.

Despite earlier fears of multiple fatalities, police have confirmed just one person has died and was the sole occupant of the car.

The driver of the truck involved in the crash has survived, the northern fire communications shift manager, Megan Ruru confirmed.

Lance Kennett who owns the Bull Ring Cafe, which is at the top of a hill near the crash site, heard sirens about 3am but says he didn't realise a crash had happened so close to his business.

There aren't too many crashes on that stretch of road, he says.

"It's not overly steep. It drops down into an area where there's a bridge and then goes up the other side. I can't really tell you what the grade is."

Lance he can see a crane truck and several police cars at the top of the hill.

Jillian Kerley, a local who lives 200m away from the scene of the crash, says she heard a loud bang and arrived to see the car stuck under the truck.

She says a fast-developing fire prevented her from getting close to the vehicles.

"It was just a wall - a sheet of flame up the front of the truck."

She says the truck driver climbed out of his cab and told them to stand back.

"So we all moved back a bit further and, yeah, flames were up over the cab of his truck and you could see that [there was] no way anyone could survive in that car."

Jillian says the truck driver, who survived, told her the driver of the car had come across the centre line and lost control going round the corner.

Meanwhile, SH1 at Atiamuri in South Waikato has now reopened to traffic after being shut for hours after the crash.