No injuries have been reported.
Roy Spooner, a local resident who lives 100 metres away from the site said the crash was loud.
"It woke me up. There was a loud crash. My neighbours live very close to that bridge. One of my concerns at the time was that there was property damage or threat to human life because it was so close to their house."
Officers are currently at the site of the derailment on Highway 537 in Wanup, Ont., 25 kilometres south of Sudbury. In addition, the Transportation Safety Board of Canada has sent a team of investigators to the scene.
Five Canadian Pacific cars carrying what police are calling "various consumer products" fell into the river.
"The river is flowing rapidly right now because the water is very high. Not too far down stream from where the bridge broke there are some rapids. And if the cars were to form across the river, they may form a dam which could cause flooding," said Spooner.
Local residents who live downstream of the derailment are being advised by police not to consume the water or swim in it because of the "potential of small-scale contamination."
"There is no immediate threat to public safety from a release of hazardous goods," police said in a statement.
The highway is currently closed to all traffic and motorists are being asked to use an alternate route.