The JLA, the RNLI’s St Helier inshore and all-weather boats, as well as lifeboats from St Malo and Granville, were all sent to the scene west of Chausey.
Two helicopters, the Channel Islands Air Search plane, a French police cutter and fishing vessels have all been involved in the search.
According to French officials leading the search, the alarm was raised just after 8.15am after a person working on the Mascaret III lobster and crab vessel fell overboard. They added that the water temperature in the area is around 10°C.
Le Télégramme, a Brittany-based newspaper, is reporting that the casualty is a man in his 30s.