Five Americans were among the dead, an official familiar with the investigation told ABC News. One of the victims was a child.
The bus was carrying tourists from two Royal Caribbean cruise ships that departed from Florida.
VIDEO FROM THE SCENE
Seven Americans and two Swedes were among the injured, said Vicente Martin, spokesman for the Quintana Roo state Civil Defense agency.
The bus ended up on its side in vegetation along the two-lane road. Video taken after the crash showed some survivors lying on the pavement and others walking around.
One body lay on the roadside covered by a white sheet or other object, as the crash scene was cordoned off with yellow police tape.
Investigators were working to determine the cause of the crash, which occurred as the bus was on its way to the ruins at Chacchoben, about 110 miles south of Tulum.
Chris Brawley, a passenger on the Serenade of Seas, was on a bus headed to the same Mayan ruins when they came on the scene minutes after the accident.
It was shortly after 9 a.m. and a convoy of buses from the cruise port at Mahahual was headed to Chacchoben, he said. They had been on the road for about 35 to 40 minutes before the accident.
Brawly 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, which happened on a narrow, two-lane road with no shoulder or guardrail.
The Associated Press contributed to this report.