THE Spanish navy has seized an American treasure-hunting ship it suspects of stealing more than $A570 million worth of gold and silver from a sunken Spanish galleon.

A navy corvette blocked the path of the Odyssey Explorer after it left the safety of Gibraltar, and threatened to open fire when the captain refused to let officers board.

The warship, flanked by vessels from the Spanish Civil Guard, escorted the Odyssey Explorer to the Spanish port of Algeciras so police could search it.