A large fire in Christchurch last night was probably caused by fireworks, says the Fire Service.

The blaze on Canterbury's Port Hills was extinguished at 1.30am today, but not before 35 firefighters were called to the scene to combat it.

Firefighters were called to burning tussock near the Sugarloaf transmission station at about 9pm yesterday and spent nearly five hours putting it out.

The Fire Service says the blaze is being treated as suspicious and a Fire Service spokesman said they were "leaning towards" blaming the fire on wayward fireworks.

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Four fire engines, four water tankers and a command unit were sent out at the fire's peak, and six firefighters patrolled the scene overnight after 2am.

An investigation will get under way this morning.

The Fire Service at this stage believes the blaze covered 20,000sq m.