Louis-Antoine Paquin, a spokesman for CN, said the freight train was travelling from Halifax to Montreal and wasn't carrying any dangerous goods.
Paquin said two locomotives as well as two cars carrying grain came off the rails early Sunday in Montreal's St. Henri district — but all of them remained upright.
"There was a fuel leak from one of the locomotives as a result of the incident," Paquin said.
No one was injured in the accident and the cause of the derailment isn't yet clear, he said.
CN and the federal Transportation Safety Board were investigating.
Andre Menard, a spokesman for Quebec's environmental emergency agency, said roughly 2,000 litres of diesel spilled from the locomotive and most of it was recovered.
The agency had earlier estimated that 3,500 litres had spilled.
Menard said the spill didn't cause any major problems.
"From an environmental perspective, it's a situation that can be easily fixed," he said, explaining the spill occurred far from the sewer system and water supply.
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