A large hole has been ripped in the hull of the Cook Strait ferry Kaiarahi.

Wellington harbourmaster Grant Nalder says the hole above the waterline in the Interislander ferry "looks quite dramatic".

"You can actually see through to the other side of the ship."

The ferry was damaged as it came into the berth in Wellington at 10pm on Sunday.

Grant says the gash in the Kaiarahi was about one metre across.

"It's obviously not good for the ship but it is high up on the hull, it's away from the waterline and it happened as it came into the berth.

"The ship itself is quite safe in the harbour - there's no risk there - but they've got a bit of work to do before it can resume service."

The hole was about one metre across, the harbourmaster says. Photo: Supplied / Regan Ingley.

Last week, a Bluebridge ferry had to turn back after it hit a wharf as it was leaving Wellington, causing a dent and a small hole in the hull.

The Connemara hit the southern end of Glasgow wharf in Wellington on November 8, and was sailing towards the entrance to the channel when the operator StraitNZ decided it should turn back.

Grant says at the time risk had been low given the size of the hole, its height above the water, and that it was going into a relatively small compartment.

"I haven't got a good reason why you get two of them a week apart," Grant told Morning Report on Monday.

"It's unconnected events that happen around the same time.

"Over the life of all the ferries, they're in and off the berth so often that you do get things go wrong and damage does occur."

It was a different wharf and a different part of the port, and there was no problem with the wharf itself, he says.

"This was the ship making contact with it, the wharf just sat there and was a wharf - it didn't do anything strange or unusual.

"But for some reason the ship landed in a different place than usual with a bit more force than intended. It was a little bit gusty around that time."

Interislander says the ferry had been damaged when it came into contact with a fender on the wharf and the relevant authorities had been informed. .

"An internal investigation is under way and we will be able to comment further when that is completed," Interislander operations general manager Duncan Roy says in a statement.

"We are working to move passengers and commercial customers to alternative sailings and are putting on additional sailings of our other ferries."

The Transport Accident Investigation Commission (TAIC) is gathering information and has not yet made a decision on whether to investigate the damage to the Kaiarahi or the Bluebridge ferry Connemara.

The Kaiarahi was damaged as it came into berth in Wellington on Sunday night. Photo: Supplied / Regan Ingley.

Grant says he and Maritime New Zealand were notified on Sunday night, and Interislander would investigate the accident.

Interislander would have to get approval before the ferry could leave from Aotea Quay.

"All the repairs will have to be signed off before the ship can resume sailing."

Asked about passenger confidence leading into the holiday season, he says there was never any good time of year for something like this, and especially not going into peak times.

The ferry operators are going to be "somewhat more on edge" and very aware of this over the coming weeks, to make sure they could provide their service over the busy time, he says.

Bluebridge Cook Strait ferry Connemara had a small hole in its hull after it hit a wharf in Wellington on 8 November. Photo: RNZ / Angus Dreaver.

RNZ