The giant November 2016 earthquake has snapped the top decks from a sunken Soviet cruise liner in the Marlborough Sounds.

The magnitude-7.8 tremor of November 14 last year pummelled the upper east coast of the South Island, cutting off the tourist mecca of Kaikoura, and causing its seabed to rise up to 2m.

It's also had an incredible impact on the wreck of the Mikhail Lermontov cruise liner which sank in Port Gore, at the northern end of the Marlborough Sounds, on February 16, 1986.

Go Dive Marlborough owner Brent McFadden, who has dived the world-renowned wreck thousands of times, noticed its damage just two days after the quake.


He found the top three decks of the 155m, 20,000-tonne Mikhail Lermontov had been jolted off in the force of the shaking and water force.

"With the ship jumping up and down, and the water pressure holding those decks in place, it was just enough to pop all the flanges, rivets or bolts holding the sundeck to the boat deck and it shored them off and it dropped down," McFadden said.

"The ship has always been pretty solid ... It's quite surprising that it's made such a change."

The wreck attracts divers from all over the world, keen for a look through the Lermontov, owned by the Soviet Union's Baltic Shipping Company and one of the biggest cruise ships to sink since the Titanic.

It had been carrying 409 mostly Australian passengers and 330 crew on its New Zealand cruise, billed as "The Two-Week Cruise of a Lifetime".

Under the command of Captain Vladislav Vorobyvev, it had left Sydney earlier in the month, and was heading for Milford Sound when disaster struck.

Captain Don Jamison, the Marlborough Harbour Board harbourmaster, pilot and acting general manager, was tasked with guiding her out of the Marlborough Sounds.

Inexplicably, the over-worked, fatigued Captain Jamison directed the helmsman to steer between Cape Jackson and the lighthouse, barely 460m from shore.

Passengers reported hearing a thud around 5.37pm.

Local fishermen and recreational boaties responded to the captain's urgent mayday call and helped save hundreds of lives.

Only one person was killed: a 33-year-old Russian engineer.

Given its shallow depth, with dives ranging from just 12m at the top of the wreck, down to 36m, along with its sheltered location, McFadden takes tours through it almost every day in the busy summer season.

He's dived it every day since the quake and has old customers returning to see the new damage and changes.

"It's the only diveable cruise liner in the world that's in recreational diving depths and we get people from all around the world, whose passion is diving wrecks, including people who have actually dived on the Titanic, who say its one of the best wrecks they've dived," he said.

The damage has allowed more light into new areas of the ship and sealife, including schools of tarakihi, have flourished.

"It's enhanced the experience in some ways but it's a bit sad to see it breaking apart," McFadden said.