Carnival Cruise Passenger Goes Overboard Off Mexican Coastline, False Alarm

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.

Folks on board tell us the passenger was watching dolphins near the back of the boat when they went overboard. It's unclear how they ended up in the water.

The Carnival Radiance sails from Long Beach, CA to Mexico ... and the ship was on its way back to Long Beach when the passenger went overboard.

The company tells TMZ ... "The Carnival Radiance crew is responding to an overboard alert off the coast north of Ensenada, Mexico. The ship is returning to where there was a potential sighting of an individual in the water to conduct a rescue operation. ... This is still a developing situation."

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.