The Keystone pipeline in the US has been shut after more than 14,000 barrels of crude oil spilled into a creek in Kansas.
The pipeline transfers crude oil from Canada to Texas, US.
The operator of the pipeline said it responded after alarms and a detected pressure drop in the system and isolated the affected segment.
In a statement, TC Energy said: “Our primary focus right now is the health and safety of onsite staff and personnel, the surrounding community and mitigating risk to the environment.
“We immediately activated our emergency response procedures and we have established environmental monitoring, including around-the-clock air monitoring.
“Our response efforts will continue until we have fully remediated the site.”
Responding to the news, Ed Markey, US Senator for Massachusetts, commented: “I am outraged but not surprised by the news of yet another oil spill from the Keystone pipeline. We have seen the same story play out year after year as they dangerously transport some of the dirtiest oil on the planet.
“We need answers and we need accountability now.”