Both authorities and company officials said no injuries were reported and no evacuations of surrounding neighborhoods were ordered.
All workers at the plant have been accounted for, Sunoco Inc.
spokesman Thomas Golembeski said. The fire had not been put out but was contained.
He said the company was monitoring air quality every hour and the readings indicated that "the situation is safe."
New Castle County, Del., county councilman John Cartier said he could see the flames from his home at least three miles from the refinery and he felt the blast.
"It was almost like seismic," he told The (Wilmington) News Journal. "My house was rocked. It was a big large boom."
Authorities were still trying to determine what caused the explosion, which occurred at the refinery's ethylene complex.
Ethylene is a feed stock used in the production of plastics. A Sunoco chemical plant adjacent to the refinery produces polypropylene.
Golembeski said the explosion and fire was contained to the ethylene unit inside the refinery and did not affect the chemical plant.
But some refining production in other units was affected, and he said the company was working with two of its upriver refineries - at Philadelphia and Westville, N.J. - to "optimize production" and meet customer demands.
He did not specify how much production was affected at facility that processes about 175,000 barrels of sweet crude oil per day into various petroleum products such as gasoline, jet fuel and home heating oil.
According to the most recent U.S. Department of Energy ranking of the nation's 150 operable refineries, Marcus Hook was ranked 39th for total production.
The refinery sits on a 781-acre site along an international seaport, and it operates around the clock seven days a week with about 700 employees. It refines oil primarily from fields in the North Sea and West Africa.
NEW YORK AND TRI-STATE AREA NEWS
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