According to Vicente Martin, the civil defense spokesperson for the state, seven Americans and two Swedes are among the injured. The nationalities of the dead are yet to be announced.
"The bus clearly lost control somehow as there were swerve marks all over the road surface," Chris Brawley, a Texan on vacation, told AP.
At the time of the crash, the bus was carrying a total of 31 passengers from Miami-based Royal Caribbean Cruises. In a statement issued by the popular cruise line, it said the collision involved tourists from its Celebrity Equinox and Serenade of the Seas vessels.
"Our hearts go out to all those involved in the bus accident," Cynthia Martinez, the cruise line's spokesperson, said in a statement. "We are doing all we can to care for our guests, including assisting with medical care and transportation."
The group of tourists were heading to Chacchoben, an ancient Mayan ruin south of the resort town of Tulum, when the bus veered off the road around 10 a.m. local time.