A 350-year-old historic gun carriage was rescued Wednesday from the bed of the Thames estuary in what government conservationists described as a race against time.

The rare and well-preserved wooden gun carriage was recovered off Southend Pier in Essex from the wreck of the British 17th century warship, the London.

The warship was part of a squadron that brought back King Charles II from the Netherlands in 1660 to restore him to the English throne after the death of Civil War victor Oliver Cromwell.

The relic is the only known example of a warship's gun carriage in existence from the period, with historians saying it will provide a key to a greater understanding of Britain's sea-faring past.

Government agency Historic England launched the rescue operation to prevent the treasure from being broken up by sea currents and sea-worms that are increasing in English waters due to climate change.

The ship blew up in March 1665 after gunpowder stored caught fire while the London was on its way to take part in the Second Anglo Dutch War of 1665-7.

The waterlogged wooden gun carriage is estimated to weigh one tonne, about the same weight as a rhinoceros.

A spokesman for Historic England said: "It was discovered by divers in pristine condition in the Thames Estuary late last summer. But over the past eight months parts of the gun carriage have become at risk of breaking up due to strong currents and exposure to sea-worms."

Alison James, Historic England maritime archaeologist, said: "This 350-year-old gun carriage is in near-perfect condition but was a national treasure at risk."

The carriage was lifted from 20 metres below the waves by a 20-tonne crane barge as divers wrapped it in wet blankets to preserve the fragile wood from drying out. It will be taken by road to York where it will be conserved over the next year by the York Archaeological Trust.

John Dillon, project manager at Cotswold Archaeology, said: "The conservation of this gun carriage will give us a great insight into the English Navy during an unsettled time when Britain was emerging as a global power."

"While the hull of the ship will remain on the seabed for the foreseeable future, the recovery and display of vulnerable artefacts such as this will aid our understanding of life on board a warship 350 years ago," said Dillon.