CANCUN, Mexico -- A preliminary investigation shows thewas caused by the driver's negligence and possible speeding, a Mexican state prosecutor says. Quintana Roo state prosecutor Miguel Angel Pech Cen says the driver tried to bring the bus back onto the narrow roadway, but caused it to flip, striking a tree and other vegetation along the roadside.
CBS News' Manuel Bojorquez reports that a 78-year-old grandmother from Miami was among the victims killed in the collision. She was traveling with four other family members. Two were injured and the other two remain unaccounted for.
A U.S. embassy spokesman confirmed to CBS News that several Americans were injured in the crash.
The driver, who was among 20 people injured, was in custody.
CBS News' Don Dahler reports the bus was carrying cruise passengers to Mayan ruins in eastern Mexico when the crash occurred early Tuesday. The excursion included: the Celebrity Equinox and Serenade of the Seas.
"Our hearts go out to all those involved in the bus accident in Costa Maya," Royal Caribbean wrote in a statement. "We are doing all we can to care for our guests, including assisting with medical care and transportation."
The bus company, Costa Maya Mahahual, said the nationalities of the passengers are American, Italian, Swedish and Brazilian.
According to the tourism ministry of the Quintana Roo state government, there were 31 people on the bus.