More than a dozen fire trucks were battling a major blaze on board a ship in Lyttelton tonight.

Emergency services were called to the fire at 5.40pm.

The 60m ship was on dry dock at the Port of Lyttelton, fire communications shift manager Riwai Grace said.

Special units and 13 firetrucks from all over Christchurch and surrounding areas were called in the fight the fire.

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"We have no idea how long it's going to take to extinguish - it's a good one," Mr Grace said.

There had been no reports of people on board the boat.

Mr Grace said he hadn't been told if any buildings close by were being threatened by the flames.

The Lyttelton tunnel had been closed to all vehicles except emergency vehicles.

The cause of the fire was not yet known, he said.