Washington, Dec. 9: Canada's TC Energy shut its Keystone pipeline in the United States after more than 14,000 barrels of crude oil spilled into a creek in Kansas, making it one of the largest crude spills in the United States in nearly a decade.

The cause of the leak, which occurred in Kansas about 20 miles south of a key junction in Steele City, Nebraska, is unknown. It is the third spill of several thousand barrels of crude on the pipeline since it first opened in 2010.

The 622,000 barrel-per-day Keystone line is a critical artery shipping heavy Canadian crude from Alberta to refiners in the US Midwest and the Gulf Coast. It is unclear how long the closure will last.

There have been no effects on drinking water wells or the public, the US Environmental Protection Agency said in a statement, though surface water of Mill Creek was affected. It sent two coordinators to the site to oversee TC Energy's response and evaluate the cause of the spill.

Keystone shut the line at about 8 p.m. CT Wednesday (0200 GMT Thursday) after alarms went off and system pressure dropped, TC said in a release. It said booms were being used to contain the spill.

"The system remains shut down as our crews actively respond and work to contain and recover the oil," the release said.

According to US Pipeline and Hazardous Materials Safety Administration (PHMSA) data, this would be the largest crude oil leak since a Tesoro pipeline leaked more than 20,000 barrels of oil in North Dakota in October 2013.-Agencies