(Reuters) - Marathon Petroleum Corp's 106,000 barrel-per-day refinery in Detroit, Michigan is reported to have released an unknown chemical into the atmosphere on Saturday at 0700 hours local time, according to an unidentified caller cited in a filing with national pollution regulators.

"The material is causing nausea, burning eyes, and difficulty breathing to local residents," the filing with the U.S. National Response Center said.

The company said on Friday it had begun shutting down the entire refinery for a 70-day planned turnaround that will tie in units from a $2.2-billion heavy oil upgrade project.

(Reporting By Shruti Chaturvedi in Bangalore; Editing by Clarence Fernandez)