No one was seriously hurt after a passenger started a fire on a TTC bus on Yonge Street north of Bloor Street early Wednesday. (CBC)

A TTC bus was reduced to a charred shell after a passenger started a fire aboard the vehicle early Wednesday morning in downtown Toronto, police say.

The blaze broke out around 2:30 a.m. on Yonge Street just north of Bloor Street. No one was seriously hurt.

A passenger started the fire after getting into an argument with a woman aboard the bus, Toronto police said. Firefighters fought the blaze and managed to put it out shortly afterward.

The suspected arsonist fled the scene in a taxi, police said.

Police described the suspect as black, six feet tall, of medium build, with short black hair and a goatee.

He was last seen wearing a beige long-sleeved unbuttoned shirt, an orange shirt with white print on the front, beige khaki pants, a black belt and white runners. He was carrying a green or dark-coloured knapsack.

Investigators are appealing for witnesses, especially the taxi driver, to contact police.