According to the Winnipeg Free Press newspaper, 37 crude oil cars derailed at 3:30 a.m. local time on Saturday (09:30 GMT) near the town of St. Lazare, located near the border with Saskatchewan province.
The incident reportedly occurred along one of the busiest Canadian rail lines.
CN Rail spokesman Jonathan Abecassis said that the exact volume of spilt crude oil remained unknown, but the spill had not contaminated the nearby Assiniboine River.
"There is no risk of contamination to the Assiniboine River … A number of provincial agencies are involved in the response to this incident, but CN Rail is leading the cleanup", a spokesperson for Manitoba’s Sustainable Development department said.
There are no reports about any people killed or injured in the incident. Causes of the derailment remain unknown.