Video footage captures explosion at Philadelphia-area oil refinery from CNBC.

An orange fireball filled the sky in Philadelphia early Friday after an explosion at an oil refinery in the southwest part of the city.

From Pennsylvania to New Jersey, there were reports of homes shaking, as people awoke to a smoke-filled sky and orders to shelter in place.

No significant injuries were reported, according to the Philadelphia Fire Department, which was working to put out the fire Friday morning.

Firefighters responded to a report of an explosion around 4 a.m. at Philadelphia Energy Solutions, a refining complex near the Schuylkill River between the city’s international airport and downtown. The complex includes two refineries, which together can process about 335,000 barrels of crude oil per day. It is the largest oil refining complex on the Eastern Seaboard, according to the company.

The Philadelphia Fire Department confirmed that there had been a “smaller fire” at the facility earlier this month, on June 10.

A spokeswoman for Philadelphia Energy Solutions did not immediately respond to a request for comment. The company has struggled with debt and emerged from bankruptcy last year, The Philadelphia Inquirer reported.

On Friday, officials discovered a fire stemming from a vat of butane, a colorless gas that is highly flammable, according to Craig Murphy, a deputy fire commissioner with the Philadelphia Fire Department, who spoke at a news conference Friday morning.

“The fire is not under control yet,” he said.

He said one employee had complained of chest pains, but did not need to be taken to a hospital.

Videos on social media showed an enormous fireball lighting up the sky and continuing to burn after daybreak. It could be seen from highways and homes, in a city of more than 1.5 million people.

The Philadelphia Fire Department said about 120 employees were on site, working with firefighters from the facility. By about 7 a.m., the shelter-in-place order had been lifted but officials advised commuters to avoid the area.

From 2011 to 2015, fire departments responded to an average of nearly 38,000 fires at industrial or manufacturing properties in the United States each year, according to the National Fire Protection Association.