A medical problem may have precipitated a dramatic crash involving an out-of-control TTC bus.

The bus swerved, smashing into a median, a light pole, and several parked cabs before hitting a tree and coming to a stop nearly a kilometre away from where the crash initiated near Yonge St. and York Mills Rd.

The cabs were hit on the other side of the street as the bus ended up travelling in the wrong direction along York Mills.

It's believed the bus driver may have suffered a seizure or some other medical problem before losing control of the vehicle at about 3am Tuesday.

"The cabs were my biggest concern," said witness Phillip Albuquerque. "I didn't think there (could) possibly (be) something wrong with the driver. He was unconscious but breathing. Soon after the paramedics were there and everything was fine."

Two cab drivers and the TTC driver were taken to hospital to be treated. Their injuries aren't life threatening. Fortunately there weren't any passengers on the bus at the time.