A major search is under way for two divers presumed dead after they disappeared while exploring a shipwreck off the coast of Cornwall. The men failed to return after they had been exploring the wreck of HMS Scylla, which was sunk in 2004. James Instance, of Falmouth coastguard, said authorities believed that the pair had died but this was yet to be confirmed. The search operation off Whitsand Bay began when the coastguard was alerted by a call at about 7.45pm on Friday from a dive party exploring the Scylla. A third diver managed to reach the surface and is being treated for decompression at DDRC Healthcare, a specialist diving medicine centre, in Plymouth. The search continued through the night into the early hours of Saturday. Instance told BBC News: “Three people had been undertaking a dive yesterday afternoon into the early hours of yesterday evening. There had been an issue below surface while they were exploring the wreck. “We swang into action a search and rescue plan involving the rescue helicopter from Newquay, the Looe and Plymouth inshore lifeboats, Plymouth all-weather lifeboat, a police launch and other vessels. “The dive boat also remained on scene. We were unable to locate or find anybody. Our thoughts are with the people who were in the dive party who are dealing with what is a very traumatic experience.” He said leisure divers were being asked to stay away from the Scylla while the recovery effort was ongoing. The Scylla was sunk to create an offshore reef, which is home to about 250 species. In 2007, two divers from Gloucestershire died while exploring it. Then in 2014, divers were warned not to enter the wreck because of hazardous conditions identified by the National Marine Aquarium. It is not clear if the two divers who went missing on Friday had entered the Scylla.