An 18-year-old has admitted shooting fireworks out the window of a car, which started a $46,000 fire in rural Canterbury.

​The fire at a property on Newtons Rd, West Melton, burnt several mature pine shelter belts, part of an ornamental garden hedge, and a ride-on lawnmower.

Thomas Tecwyn Williamson, a fencer from Darfield, pleaded guilty on Tuesday to the charge of recklessly causing the damage on November 3 when he appeared at the Christchurch District Court. He will be sentenced next year so he can travel to Japan for a ski course.

IAIN MCGREGOR/STUFF Barto Ashman, 9, among trees destroyed by a blaze started by fireworks shot from a car window.

The fire came close to the victims' house before it was brought under control, with scorching and damage to a window awning from falling embers, police prosecutor Bronwen Blackmore said.

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Homeowner Rebecca Ashman said the family was lucky to come out of the fire unscathed. Flames over 10 metres high could be seen licking above the pine trees at the front of the property.

IAIN MCGREGOR/STUFF Rebecca Ashman's home was under threat as a hedge and trees burned destroyed by fireworks. She and daughter Aurelia, 6, examine the damage.

The flames crept within metres of the dog's kennel before her husband saved it. Several hedge rows and gardens were damaged, and a ride-on lawnmower was incinerated.

FIRE FORCES FAMILY FROM HOME

Williamson was a passenger in a car that pulled over on Newtons Rd. Williamson lit and fired fireworks out the window as another car containing friends went by. The cars had been travelling in convoy around the area.

IAIN MCGREGOR/STUFF Sprinklers dampen down hotspots on their property.

Some of the fireworks hit a hedge on the opposite side of the road. A witness yelled at them and both vehicles sped off.

The fire in the vegetation caught hold quickly, in the warm weather and strong winds. Emergency services took several hours to put it out, and the property owners moved out of their house overnight while fire crews dampened down and monitored the blaze.

PUBLICITY PROMPTS CONFESSION

Police publicised the description of the two vehicles – a BMW and a Mazda RX8 – and Williamson went to the police three days later to say he fired the fireworks.

He said he shot the fireworks into the air above the other car. Some shots went near the hedge, but he did not think they went into the hedge. He said it occurred to him later that he should have checked if the shots started a fire.

Reparation claims are expected from the victims' insurance company, Fire and Emergency New Zealand for fighting the fire, and for the removal and replacement of trees not covered by the victims' insurance.

FOUR YEARS SAVING FOR JAPAN

Defence counsel Gerard Thwaites asked for an eight-week break before sentencing, because Williamson was helping the victims with the damage and he was about to travel to Japan to do a course for a ski registration ticket.

He said Williamson had saved for four years for the trip and was due to leave next Wednesday. The teenager had made a massive mistake with disastrous consequences.

Blackmore said the police originally wanted Williamson to surrender his passport, but now he had pleaded guilty they had no objection to him travelling to Japan.

"He won't be a flight risk," said Thwaites. "His mother and father are in court."

Judge John Macdonald remanded Williamson on bail for sentencing on March 20. He asked for a pre-sentence report, a reparation report and a referral for a restorative justice meeting with the victims.