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Colombia is urging people to help recover billions of dollars in gold and silver from a sunken Spanish galleon discovered off its coast in 2015.

The vessel, the San Jose, belonged to Philip V of Spain and sank in 1708 during a battle with the British navy.

Colombian President Juan Manuel Santos now hopes to retrieve the "holy grail" of treasure believed to be on board.

Though no official value has been put on the bounty, estimates range from $1bn (£760m) to $10bn.

Mr Santos is looking to form a public-private partnership with an investor and anyone willing to assist in the retrieval of sunken items, which were probably extracted from Spanish colonial mines in Peru and Bolivia.

Colombia then plans to build a museum for the recovered pieces and a laboratory to study and conserve the material, the president said.

Details of the legal and scientific requirements for joining the partnership are expected to be announced at a hearing in the Caribbean city of Cartagena on Friday.

Treasure hunters have long shown an interest in the San Jose, which is described as the holy grail of shipwrecks as it was said to be carrying one of the largest amounts of valuables ever to have been lost at sea.

Items are thought to include gold, silver, gems and jewellery collected in the South American colonies to finance the Spanish king's war effort.

Spain has sought an amicable agreement with Colombia over the ship and its contents but has also said that it is prepared to defend its interests at the UN if necessary.

In 2013 Colombia approved a law to define sunken ships found in its waters as national heritage.

Colombia estimates there are up to 1,200 such wrecks off its coast.