At least 12 people died after a bus carrying cruise ship passengers from South Florida to the Mayan ruins in eastern Mexico flipped over a highway early Tuesday.

The nationalities of those who died have not yet been confirmed. Among those injured were seven Americans and two citizens of Sweden, Quintana Roo state civil defense spokesman Vicente Martin said, according to the Associated Press. The U.S. Embassy in Mexico is monitoring the situation.

A U.S. Embassy spokesman said in an emailed statement that officials “are in contact with local authorities and are working with them to determine if there were U.S. citizens on board.”

“We express our condolences to all those affected by this tragedy.”

The cause of the crash, which occurred on the Mahahual-Cafetal highway in the southern part of Quintana Roo, is being investigated. The bus was heading to the ruins at Chacchoben, 110 miles south of Tulum, Mexican authorities said.

The bus carried 31 passengers, according to a statement from government officials in Quintana Roo. Among the passengers killed was a girl under 18, officials said. At least 18 people were injured.

Those injured were taken to hospitals in Bacalar, Chetumal and Tulum, officials said.

The majority of the passengers came from two ships belonging to Miami-based Royal Caribbean Cruises: the Celebrity Equinox and the Serenade of the Seas, which are both seven-night Caribbean cruises, the company said in a statement. About 23 passengers on the bus came from the Celebrity Equinox, which left Saturday from Port Miami, while four came from the Serenade of the Seas, which departed Friday from Port Everglades in Fort Lauderdale.

“Our hearts go out to all those involved in the bus accident in Costa Maya,” the company said. “We are doing all we can to care for our guests, including assisting with medical care and transportation.”

In addition to the passengers, the bus was carrying a driver and guide, Costa Maya Mahahual, the bus company involved, said in a statement to the AP.

Video images from the scene showed the bus on its side off the two-lane highway, according to the AP. Some survivors lay on the pavement while others walked around.

Follow the Bangor Daily News on Facebook for the latest Maine news.