Police from Muang Samut Sakorn Police Station said they were informed of the accident on Wednesday night and rushed to the scene where they found the damaged tour bus.
Police said the falling rubble had cracked the bus's windshield.
The driver reportedly told police that the cement rubble fell from an excavator bucket into the bus's windshield while he was passing the construction site in the Muang district of Samut Sakhon province on Rama 2 Road.
He said a piece of windscreen glass flew on his face, causing injuries, and his right arm also suffered injuries from the falling rubble.
The driver said he steered the vehicle to the side of the road soon after the accident and informed the police.
All the people in the vehicle were transferred to another bus to transport them to their destination, the driver said.
Police have brought the bus driver, the head of the construction site, and witnesses to the police station to conduct further investigation.
The Rama 2 Road is notorious for “never-ending” construction work that have caused several road accidents. The road has seen at least seven accidents over the past year.