Nov 21 (Reuters) - U.S. officials said on Tuesday seven energy companies have been impacted by an oil discharge near Main Pass Oil Gathering Co's pipeline system in the Gulf of Mexico that is estimated to have released more than a million gallons of crude oil.

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.

"Seven producers affected and those producers are currently shut in," Brian Domangue of the Bureau of Safety and Environmental Enforcement said during a press briefing.

Officials said investigations and surveys were ongoing to determine the source of the discharge, but added that there were no reported injuries or shoreline impacts so far.

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

The officials also said it was yet to be established if Third Coast Infrastructure, which owns MPOG, is responsible for the spill.

"They're suspected responsible party but we won't know until we find the source which is why we keep referring to them as the responding party," said Captain Kelly Denning, deputy commander, sector New Orleans. (Reporting by Mrinalika Roy in Bengaluru; Editing by Shounak Dasgupta)