Two divers are presumed dead after not returning to the surface.
The divers had been in a group exploring HMS Scylla which was sunk in 2004 off the Cornish coast.
Emergency services were called out by a member of the team.
The search continued near Whitsand Bay into the early hours of the morning.
James Instance from Falmouth Coastguard said the pair are feared to be dead but this hasn’t been confirmed.
Mr Instance said:
“We swung 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.”
HMS Scylla was sunk to form a reef.
It is a popular diving location.