One person was killed and another 12 were injured in southwestern Ontario early Sunday when a bus left Highway 401 and rolled over into a ditch, police said.

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Police said the bus went airborne and rolled into the highway's south ditch. ((Ivy Cuervo/CBC) )

Provincial police in Oxford County said the vehicle — operated by McCoy Bus Service based in Kingston, Ont. — was travelling east near Woodstock around 6 a.m. ET when it left the road, became airborne and flipped over into a ditch. It was carrying some members of the Napanee, Ont., fire department and their families.

Darlene Goodfellow, 49, the wife of one of the volunteer firefighters, was pronounced dead at the scene, police said. Twelve people, including the fire department's chief and the bus driver, were taken to hospitals in Ingersoll, Woodstock and London.

Four of the injured people were previously hurt in a separate crash Saturday night on Highway 401 near London. The bus involved in Sunday's crash had picked them up, along with family members, to take them home to Napanee, near Kingston, after they were released from hospital.

"We are all very shaken by this chain of events," said Napanee Mayor Gordon Schermerhorn. "Our small community is pulling together to help those involved in this tragic accident."

5 firefighters in both crashes

In all, five firefighters from Napanee were returning from a competition in Windsor, Ont., when they were involved in the two accidents.

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The badly damaged bus flew over a concrete median on Highway 401. Investigators have not determined why. ((Ivy Cuervo/CBC) )

Investigators arrived on the scene of Sunday's crash, at the western junction of Highways 401 and 403, to find the vehicle lying on its side in the ditch. The front portion of the bus was sheared off and remained on the highway.

Police have not determined what caused the disaster.

"Officers are with the injured parties at the hospital and will be speaking with them," Const. Michelle Murphy of the Oxford County OPP said.

Police kept Highway 401 eastbound closed for up to six hours while they investigated the crash, and traffic was rerouted onto Highway 403.

With files from The Canadian Press