A leak from the Keystone pipeline that spilled up to 588,000 gallons of crude oil into a US stream was being contained on Friday, US officials said.
If the estimate on the size of the spill holds, it will be the largest crude spill in the United States since 2013, according to the Pipeline Safety Trust, which promotes pipeline safety.
Canadian-based TC Energy, which operates the pipeline, detected the leak on Wednesday night in Kansas and immediately halted the flow of oil through the pipeline.
"The affected segment of the Keystone Pipeline System remains isolated" and spillage downstream "is contained," the company said in a statement.
The cause of the discharge was still being investigated on Friday by authorities, the Environmental Protection Agency said.
Transportation Secretary Pete Buttigieg tweeted that authorities "are monitoring and investigating the... leak."
The Environmental Protection Agency said TC Energy had deployed vacuum trucks and oil skimmers, and built an earthen dam four miles downstream from the rupture site along Mill Creek. It said efforts to deal with the spill "will extend into the next week."
The Keystone Pipeline transports oil from the western Canadian province of Alberta to several destinations in the United States. It transports about 600,000 barrels per day under normal circumstances.
Oil prices temporarily rose Thursday after the leak was announced but fell again.
The impact of the incident on the energy market will depend on how long flows of crude are suspended along the Keystone, which brings oil to, among other places, Cushing, Oklahoma, where West Texas Intermediate, the benchmark US crude, is traded. (AFP)