Possible arson behind Christchurch hay barn fire

Two fire trucks and 21 firefighters battled the blaze at a barn on Spencerville Rd near Kaiapoi overnight. File photo / Glenn Taylor

A large fire at a hay barn north of Christchurch overnight is being treated as suspicious.

Fire crews were called to the barn on Spencerville Rd near Brooklands about 1.30 this morning to find it well alight.

Two fire trucks and seven water tankers were sent to contain the blaze.

A fire investigator would be at the scene today, Fire and Emergency NZ southern shift manager Andrew Norris said.

There was no logical explanation for how the fire started, and there had been reports of a suspicious car in the area, he said.

Twenty-one firefighters had spent the morning containing the blaze and pulling apart about 150 large bales to dampen down any hot spots. The fire was now out but crews remained on scene.

"We've just crews dampening down hot spots and pulling it apart, because it will still be smouldering."

The fire was in a rural area, so there was no threat to other properties.