The 67-mile long pipeline was closed by Main Pass Oil Gathering Co (MPOG) on Thursday morning, after crude oil was spotted around 19 miles offshore of the Mississippi River Delta, near Plaquemines Parish, southeast of New Orleans.

"Overflight teams observed visible oil Friday moving southwest away from the Louisiana shore," the Coast Guard said, as oil recovery efforts continued and underwater devices surveyed the pipeline to find the leak's source.

While the exact volume of discharged oil was not known, the Coast Guard, which was leading the clean-up, said initial engineering calculations placed the volume of the leak at 1.1 million gallons, or 26,190 barrels.

It added that there were no reported injuries or shoreline impacts so far, and the cause of the leak was under investigation.

The U.S. Environmental Protection Agency said on Friday that the Coast Guard had activated the National Response Team, comprising 15 federal entities responsible for coordinating the response to oil pollution incidents.

Third Coast Infrastructure, which owns MPOG, declined to comment on Friday and referred questions to the Coast Guard.