Passengers on the ship told said they woke up to the sound of sirens at around 3 or 4 a.m. Wednesday, and one heard a request for medical assistance on one of its decks, according to KHOU.

The FBI is investigating the death of a Texas man on the Carnival Dream cruise ship, with no trauma signs evident.

According to Carnival's schedule for a six-day cruise, the Dream left Galveston last Sunday, July 20. By Wednesday, the ship was traveling between Belize and Cozumel, Mexico, when multiple passengers reported hearing alarms go off in the middle of the night.