The pipeline crew are responding to a release at its Sumas Pump Station in Abbotsford, British Columbia, after an alarm was received early in the morning, Trans Mountain Corp said in a statement.
The estimated volume of oil spilled is not available, but the spill has been contained and cleanup is underway, the company said.
While there is no threat to the community, the pipeline remains shut and an investigation into the cause of the spill is ongoing, Trans Mountain said.
The pipeline company delivers about 300,000 barrels of crude oil and refined products every day through 1,150 kilometers of pipeline in Alberta and British Columbia, and 111 kilometers of pipeline in Washington state, according to its website.
The Transportation Safety Board of Canada (TSB) said in a separate statement it had deployed an investigator to the spill site to gather more information.
The Canadian government bought the Trans Mountain pipeline from Kinder Morgan Canada in 2018, as it faced regulatory and legal hurdles to expansion.