Fort Jervois, built in the 1880s, was damaged by the Canterbury quakes in 2011.

Urban explorers have sneaked into a quake-damaged abandoned island fortress steeped in Maori and New Zealand settler era history.

Members of the group Urbex Central, who have made waves with visits to abandoned film sets, Christ Church Cathedral and derelict buildings, swam the short distance to Ripapa Island, off the coast of Lyttelton in the South Island.

Ripapa Island is an important heritage site off the south shore of Lyttelton Harbour but has been closed to the public since the Canterbury quakes.

The Urbex Central group posted photographs of their visit to the island, which was the site of a Maori fort, known as a pa, a quarantine station and a prison during the settler era.

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Urbex Central The ''disappearing guns'' were installed in response to fears of a Russian invasion.

The explorers said they hoped the fort, ramparts and buildings could be restored for visitors.

Nestled within the fort's grounds are the remains of two cannons on revolving platforms hidden from view known as "disappearing guns," a torpedo store and a mine store.

Food is not meant to be eaten on Ripapa due to its sacred Maori history.

Urbex Central Ripapa Island in Lyttleton Harbour.

Many burial sites lie nearby and on the island.

"Another victim of the earthquakes, this historic wartime island was once used as a quarantine station, Maori fortification and a defence against Russian attacks.

"On arrival and after a short swim across to the island we navigated our way up the steep barbed wire bank.

Urbex Central Fortified ramparts at the entrance to the Ripapa Island complex.

"Once inside the fort we were met by a beautifully designed historic fort which included a labyrinth of tunnels with torpedo and mine stores.

"The two disappearing guns on the fort were completed in 1895 and were never actually used to fire a shot in their years as part of the island fortification," the Urbex post said.

The small island was home to a fortified pa in the 19th century, built by a South Island Ngai Tahu chief, Taununu.

Urbex Central The island's fort was used as a temporary prison, quarantine centre and army base.

Skirmishes were fought on the shores and on the island, which was occupied by Ngai Tahu until 1832, when the chief, Te Whakarukeruke, left to defend the settlement around Kaiapoi from a warrior, Te Rauparaha.

The Maori fort, possibly the first fortified defence in the South Island, was sacked during tribal warfare known as Kai huanga, or "eat relations" feud, in the 1820s.

The island was used a quarantine station for immigrants for more than a decade from 1873 and as a temporary prison.

Urbex Central Inside the fortifications on Ripapa Island.

Fort Jervois, a category one listed building, dates from 1886 and was built as a coastal defence in response to widespread fears of an attack by the Russian empire during tension with the British colonial empire.

Fortified defences were built elsewhere in New Zealand during the so-called "Russian scare" but the guns on Ripapa were never fired and there was no invasion.

In the 20th century, the island was used by the army during both world wars.

Urbex Central The island is steeped in New Zealand settler era history and Maori lore.

Conscientious objectors occupied the island briefly in the lead up to the outbreak of hostilities in 1914, it was used as a battery during World War One and one of the guns was restored during coastal defence preparations in 1941 but it was eventually declared ineffective.

The Department of Conservation has managed the island since 1990, closing it to the public after the Canterbury quakes.

Comment has been sought from the department and Urbex Central about the group's visit.