A truck caught fire on State Highway 1 on the Kaikoura Coast.

It is understood the blaze spread to the nearby grass.

Emergency services are on their way to the incident, which is not far from the town of Kekerengu.

An eyewitness saw cans "flying like fireworks" out of a truck and trailer unit which caught fire in Canterbury today.

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Australian man Gary Jackson was driving behind the truck on State Highway 1 near Kekerengu when he saw smoke coming from the back of the unit.

"Then flames, which were one or two feet high, started erupting up the side of the trailer unit," he said.

"The driver pulled over and disconnected the trailer from the truck.

"One of the tyres exploded off it onto the side of the road and set bush on the side of the road on fire."

Mr Jackson, who is on a dog bite prevention seminar tour, grabbed the fire extinguisher from his camper van but it was faulty.

"There wasn't any juice in it. The driver was really good at handling everything, though, and there was guys doing work on the side of the road who got their things out of the way and started directing traffic."

The Fire Service, helicopters and an ambulance were called to the incident and the road was temporarily closed.

No one was injured, Mr Jackson said.