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(3:35 p.m. EST) -- Royal Caribbean Cruises Ltd. has confirmed that several cruise passengers from Celebrity Equinox and Serenade of the Seas were killed when the tour bus they were on overturned during a port call for both ships in Costa Maya.

"The news from Costa Maya about a bus accident involving our guests is heartbreaking," the cruise company said in a prepared statement. "Our hearts go out to all those involved. We are doing all we can to care for our guests, including assisting with medical care and transportation."

The company further said 27 passengers were on the bus and that it is in contact with local authorities, in a Twitter post.

According to various news reports, at least 12 people were killed with close to 20 more injured when the cruise line-sponsored tour bus they were on flipped over on a highway early this morning. The bus was on the way to the Chacchoben Mayan ruins about 110 miles south of Tulum when the accident occurred. The cause of the accident is still under investigation.

Seven American and two Swedish passengers were among the injured; information about the deceased has yet to be released.

--By Dori Saltzman, Senior Editor