The two are among four men who had gone into the sea off the coast of Brighton in the early hours today, according to the Maritime and Coastguard Agency.
Two men managed to get back to shore and called the Coastguard just after 1 am (local time) this morning telling them that two of their companions were missing.
The agency said the search had turned into a recovery mission as there was "no chance of finding them alive," the BBC reported.
Coastguard rescue teams from nearby Shoreham and Newhaven and are searching the waters for the pair.
"The conditions for searching overnight were awful - it was pitch black and the sea was extremely choppy. It was very difficult to search," an agency spokesman said.
"The helicopter and the all-weather lifeboats searched the area overnight but started to stand down at about 04:00. They felt they had done all they could. Very sadly, nothing has been found and it is very unlikely that anything will be," he said.
