Two divers have been airlifted for medical treatment after a suspected decompression sickness incident.
The women were part of a group diving on the Manacles, a collection of rocks off The Lizard in Cornwall.
It was believed they suffered the condition, also known as the bends, after ascending too rapidly to the sea surface, coastguards said.
A helicopter from RNAS Culdrose has flown them to the Diving Diseases Research Centre in Plymouth.
Resurfacing too quickly can result in bubbles of gas forming in a diver's blood supply, which can be fatal.
The Diving Diseases Research Centre is a medical research and training charity which uses a hyperbaric oxygen chamber to treat divers suffering from the condition.