One person has died and another is in a critical condition following a crash at Fernside in the Waimakariri District.

One person died at the scene and another received serious injuries, a police spokesperson said.

A St John spokesman said one person was flown to Christchurch Hospital in a critical condition via helicopter.

Stuff reported it was a young boy that died in the crash and his father has been badly burned, with burns covering more than two thirds of his body.

Police are now investigating the circumstances around the accident.

Police were notified of single-vehicle incident on Lehmans Rd, Fernside around 4.15pm, a spokeswoman said earlier.

"There was a report a car went down a bank and was on fire," she said.

Fire and Emergency New Zealand, St John Ambulance and police were all at the scene and the Serious Crash Unit had been notified.

Christchurch Transport Operations Centre had advised road users to avoid the area while emergency services dealt with the crash.

Lehmans Rd was closed at the Priors Rd intersection and at River Rd/West Belt, the Waimakariri District Council said on Facebook.