A scuba diver has died and another is still missing after an expedition in the sea off West Sussex.
A third man in the diving party had to be flown to a decompression chamber after suffering from the bends.
Lifeboats crews were first alerted to the incident just after midday on Tuesday.
Solent coastguard, which coordinated the search, said the three divers had apparently been exploring a wreck off Shoreham.
They were diving to a depth of 63m while using the boat the Michelle Mary as their base.
It is believed the divers resurfaced too quickly after exploring the wreck.
David Williams, Solent Coastguard watch manager said: "The divers were wreck diving 15 miles south of Shoreham-on Sea when this incident began.
"We know the first diver made a rapid ascent from a very deep dive, although the second diver came up with some of his stops."
At about 1800 BST the coastguard spokeswoman said they were still searching for the missing diver.
She said: "They have been searching for five hours and they are going to carry on."
The injured diver was flown to the Queen Alexandra Hospital in Portsmouth and treated in a decompression chamber.
A police spokesman said his condition was not thought to be serious.
The coastguard has said the visibility in the area being searched was good although there were waves of about two metres.
Police said the Michelle Mary had joined in the search for the missing diver but had returned to its base in Littlehampton.
Officers are examining the diving equipment used but it is thought all three divers were experienced.