The first collision between the articulated vehicles left 30 injured while a second just half an hour later saw another 120 likewise suffer cuts and bruises.
It was not immediately clear why the buses, which run on specially designated lanes and are designed to transport some nine million people a month, had collided.
Witnesses to the second accident claimed the driver of one of the buses had been talking to his wife on his cell phone when passengers yelled out a warning the vehicle was too close to another bus.
Firefighters gave first aid to the injured, several of whom were taken to hospital.
The BRT buses will take Olympic visitors from the city center out to the western suburb of Barra de Tijuca, site of the Olympic city and a majority of events spread across four venue hubs.
Several of the bus routes are already in operation.
Bus accidents are common in Rio with passengers regularly complaining that drivers go too fast or do not keep their eye on the road.
