Two divers are believed to have died after failing to return to the surface while exploring a wreck off the Cornwall coast.
The couple dived around HMS Scylla, which was sunk in 2004 to create an offshore reef.
A major search operation in front of Whitsand Bay went off in the early hours of Saturday morning.
The James Instance of Falmouth Coastguard said they suspected the couple had died, but this was not confirmed.
HM Coastguard said it received a call at 19:45 BST on Friday after two divers were reported on a dive wreck near Whitsand Bay.
Mr Instance said: “Three people took a dive yesterday afternoon and early last night.
“There was a problem beneath the surface while they were exploring the wreck.”
One of the three divers was able to return to the surface and raise the alarm, the HM Coastguard said.
They are currently being treated for decompression at DDRC Healthcare in Plymouth.
The HM Coastguard said his helicopter was recovered from Newquay in search of the RNLI Lifeboats from Plymouth and Looe, as well as from police.
“We could not find or find anyone,” Mr Instance said.
“Our thoughts are with the people who were at the dive party who came to terms with a very traumatic experience.”
He said recreational divers were asked to stay away from the wreckage while on a recovery mission.
Two Gloucestershire divers have died in the 2007 Scylla Wrack discovery.
In 2014, divers were warned not to enter the wreckage due to dangerous conditions identified by the National Marine Aquarium.
It is not clear if the two divers who went missing on Friday went to Scylla.