Failed brakes are said to be cause of the accident, according to director Tawin Ratanawongsawat of Khon Kaen Zoo, which is 500 kilometres north-east of Bangkok.
The zoo could not immediately confirm the number of casualties.
The injured were transferred to several nearby hospitals.
Due to the zoo's hilly terrain and large area of about 3,000 acres, visitors usually take the tram or rent a private golf cart to travel around.
The zoo houses many exotic animals such as white lions and white tigers.