4:49 PM PT — A spokesperson for Carnival Cruise Line tells TMZ … “The Carnival Radiance crew responded to a potential overboard alert off the coast north of Ensenada, Mexico when some guests reported hearing a splash in the water.  The ship returned to the area where there was a potential sighting of an individual to conduct a rescue operation. In the meantime, the crew completed a full guest and crew headcount as is our standard safety protocol and all guests and crew have been accounted for. The splash could have very well been a whale but there is no way to confirm that. In any case, all on board are accounted for and the ship will resume its itinerary.”

A rescue operation is underway in the Pacific Ocean after a passenger went overboard on a Carnival cruise.

Carnival Cruise Line tells TMZ … the Carnival Radiance crew is responding to an overboard alert off the coast north of Ensenada, Mexico.

We’re told the cruise ship is returning to where there was a potential sighting of a person in the water … and we obtained video of rescue boats in the water searching for the passenger, plus footage of someone splashing around.

Carnival can’t seem to catch a break the days … as we reported, a teenage girl was found dead on a cruise ship in the Caribbean … so there’s been troubles on both coasts.