Go Dive Marlborough owner Brent McFadden says the 7.8-magnitude earthquake has created a new diving environment on the Mikhail Lermontov.

A Soviet cruise liner resting on the seabed of the Marlborough Sounds has "parted company" with its top three levels after the earthquake last year.

The force of the 7.8-magnitude earthquake caused extensive changes to the wreck of the Mikhail Lermontov, which sank in Port Gore on February 16, 1986.

Go Dive Marlborough owner Brent McFadden, who has dived the site thousands of times, first saw the changes on a trip days after the disaster.

BRENT MCFADDEN The bridge of the Mikhail Lermontov.

The top three levels of the 155-metre long ship, the jewel in the crown of the Soviet cruise fleet, had been sliced off by the movement and force of the water.

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"The bridge deck, the sun deck and the compass deck parted company with the boat deck," McFadden said.

NIWA A sonar image of the 155-metre long Mikhail Lermontov resting on the seabed in Port Gore, in the Marlborough Sounds.

"With the ship jumping up and down they actually shore off and dropped to the bottom."

Before the quake the decks had hung suspended above the seabed because of the way the ship came to rest, lying on its starboard side in up to 37m of water.

SCOTT HAMMOND/FAIRFAX NZ Go Dive Marlborough owner Brent McFadden beside one of the lifeboats from the Mikhail Lermontov, in Picton.

McFadden said a hatch cover had also popped open in the earthquake, revealing a cargo hold he had wanted to explore for years, with two shipping containers inside.

Ever since the original exclusion zone around the wreck was cleared, divers had been taking trinkets from the ship: crockery, bottles from the bars, and other mementoes.

"There were a lot of people that went through all the bedrooms and took things - it was a bit of a treasure hunt in the first year or two," McFadden said.

SUPPLIED The Mikhail Lermontov listing after hitting rocks off Cape Jackson, in the Marlborough Sounds.

The Picton dive store owner stressed that anything he took from the site went into a kind of museum, based out of a dive lodge leased by the company in the Sounds.

However, he said he once tried some Guiness he found in a bottle in one of the bars, and even after 30 years under the water it was OK to drink.

Diving through the sunken liner, named after the celebrated Russian poet Mikhail Lermontov, shot dead in a duel in 1841, could be an eerie experience, McFadden said.

BRENT MCFADDEN A commemorative plaque made for the 30th anniversary of the sinking of the Mikhail Lermontov, on February 16, 1986.

Tables and chairs bolted to the floor had become part of the walls divers passed along, with everything transformed into a kind of twilight zone green because of the algae.

Last January, McFadden and a dive group were exploring the wreck when an earthquake hit, throwing up silt and reducing visibility to almost zero.

"An earthquake on land is bad enough but under the water .... One of the guys was in the [Lermontov's] hospital and he said the walls were billowing in and out," he said.

SCOTT HAMMOND/FAIRFAX NZ One of the photos Go Dive Marlborough owner Brent McFadden has of the doomed cruise liner.

"It was a little bit like a dog shaking itself after it's come from a swim in the river, the wreck was actually jumping up and down.

"It sounded like someone had started the engines."

The Mikhail Lermontov sank after hitting rocks off Cape Jackson while it was being piloted by Marlborough harbourmaster Captain Don Jamison.

ALEXANDER TURNBULL LIBRARY The Soviet cruise liner Mikhail Lermontov berthed in Wellington Harbour, the day before it hit rocks off Cape Jackson, in the Marlborough Sounds.

One person was killed.

Jamison attempted to navigate the ship through a narrow, shallow passage between the cape and an offshore lighthouse, when it struck rocks, tearing a long gash in its port side.

The harbourmaster has never spoken publicly about his decision to take the ship through the passage, and there was criticism at the time that no formal inquiry was held.

Last year, the 30th anniversary of the sinking, McFadden and others attached a plaque to the bridge of the Lermontov, with the line '30 years amazing diving. Thank you Cpt. Don Jamison, pilot'.

"As far as wrecks are concerned, it's the most accessible cruise ship in the world, because it's within recreational depths," McFadden said.

"It's become its own ecosystem, the variety of fish in it is greater than any other dive site in Marlborough."