12 people have been killed after a bus carrying cruise ship passengers on an excursion to Mayan ruins in Mexico flipped over on a narrow motorway.

11 tourists and their tour guide died in the crash, about 300km from Cancun on the Yucatan peninsula.

A child is feared to be among the dead.

Officials say they are yet to establish the nationalities of those who were killed, but the AFP news agency reports "several foreigners" are among the dead.

A total of 20 others were injured, including seven Americans and two Swedes.

Footage of the aftermath showed some survivors lying on the pavement and others walking around.

A body could be seen on the roadside covered by a white sheet, and the scene of the crash was cordoned off with police tape.

Royal Caribbean Cruises, based in Miami, released a statement saying passengers from two of its ships - the Celebrity Equinox and Serenade of the Seas - were on the bus.

The company expressed its sympathies and said it was assisting with medical care and transportation.

The US embassy in Mexico City said it was aware of reports that several American citizens had been injured, and its officials were working with local authorities to identify the individuals involved.

Vicente Martin, spokesman for the Quintana Roo state Civil Defense agency said investigators were working to determine the cause of the crash.

Chris Brawley was a passenger on the Serenade of Seas, and was on a different bus headed to the same Mayan ruins.

They arrived on the scene minutes after the accident.

He said the sky was clear and the road was dry and he didn't see any sign of another vehicle being involved in the crash.

"The bus clearly lost control somehow as there were swerve marks all over the road surface," Mr Brawley said.