(CNN) A double-decker bus crashed in Ottawa, Ontario, on Friday, killing three people and injuring at least 20, Mayor Jim Watson said at a news conference.

The bus collided with the platform at the Westboro bus station at about 3:50 p.m. ET, he said.

Three people died -- two on the bus and one person waiting on the platform, Watson said. Twenty-three people were hurt and taken to hospitals, he said.

Ottawa Police Chief Charles Bordeleau said several people on the top section of the bus had to be freed.

Statement from Chief Bordeleau about the serious single vehicle collision at Westboro Station https://t.co/dUzjzLy1xo#Ottnews #Ottnouvelles — Ottawa Police (@OttawaPolice) January 12, 2019

He said investigators are trying to determine the cause of the crash. The driver was arrested and was being questioned by police, but the chief didn't provide details.

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