TORONTO — The killing began on a busy lunchtime thoroughfare in Toronto on Monday when a white rental Ryder van ran over a pedestrian crossing the street — then mounted a sidewalk and began plowing into people indiscriminately.

“One by one, one by one,” said a witness who identified himself as Ali. “Holy God, I’ve never seen such a sight before. I feel sick.”

By the end, at least 10 people were dead and 15 were injured, said the authorities.

The driver’s actions, they said, appeared intentional, but did not seem to have been an act of terrorism. “The city is safe,” said the Toronto police chief, Mark Saunders.