At least 12 people died when a bus carrying cruise ship passengers to Mayan ruins in eastern Mexico flipped over on a highway early Tuesday, officials said.

Seven Americans and two citizens of Sweden are among the injured, according to Quintana Roo state Civil Defense spokesman Vicente Martin, who said authorities haven't yet established the nationalities of the dead.

Video images from the scene showed the bus on its side in vegetation off the two-lane highway, with some survivors lying on the pavement while others walked around.

The cause of the accident was under investigation.