Three people were killed and nearly two dozen others were injured when a double-decker bus hit a hut in the Canadian capital of Ottawa during rush hour, city officials said.
Part of the upper right side of the bus was removed in the collision, which occurred in a busy transit station in the western part of the city.
"It is with deep sadness that I report that there were three confirmed victims, two of whom were on the bus and one that was on the platform," Ottawa Mayor Jim Watson told reporters at a press conference .
Watson also said that 23 people were injured in the collision, some very seriously, and taken to hospital. The Ottawa hospital confirmed on Twitter that it had received nine critically ill patients from the crash.
Ottawa Police Chief, Charles Bordeleau, said the bus driver was arrested and interrogated, but refused to provide further details.
"An investigation is underway on the cause of the collision," he told reporters.
Investigators were expected to be on the scene all night, with cold temperatures in Ottawa that expected to drop to -22C (-7.6 F) overnight.
"There is no doubt that time adds complexity to the scene," said Bordeleau. It is not clear whether the weather contributed to the accident.
Photos and videos of the scene showed that rescuers were responding to a number of people on the ground, while others used the stairs to unload passengers trapped on the upper level of the bus.
Bilal Gill, a passenger on the upper floor, told the CBC News that the people at the front were locked in their seats.
"There was certainly people stuck in. And there was a little blood on the floor," he said.
This is the second serious accident in recent years involving an Ottawa transit bus. A double-decker commuter bus crashed into a passenger train in September 2013, killing six people including the bus driver.