PHILADELPHIA (KDKA) – An explosion, fireball, smoke and flames that could be seen for miles.

“It looked like an atom bomb went off. The whole sky got bright orange,” an eye witness said.

A massive fire at an oil refinery in Philadelphia rattled the area and sent huge balls of fiery gas into the air.

It happened at the Philadelphia Energy Solutions Refining Complex shortly after 4 a.m. Friday in South Philadelphia.

In all, there were three explosions. Firefighters aren’t sure yet what caused the first one, but they do know it was centered in a vat filled with butane.

“Like you fill your lighter with butane. And this is from the PIO, with Philadelphia Energy Solutions. It was burning inside the vat and it’s pretty much contained to that vat right now,” said Craig Murphy, deputy fire commissioner with the Philadelphia Fire Department.

Butane is one of the products that come from the process of refining crude oil. The refinery’s in-house fire crews, as well as the Philadelphia Fire Department, have been working for hours to fight the massive blaze.

At this point, their main concern is protecting other areas of the refinery. “The fire is not under control yet. Right now, companies are making sure that the fire does not spread as best they can,” said Murphy.

Refinery employees were reportedly working somewhere close to the vat when the fire started, but fortunately far enough away that no one was seriously hurt. However, four employees did suffer minor injuries.

People reported feeling the explosions throughout suburban Philadelphia and as far away as South Jersey.

“I heard it up at home in the northeast,” one man said. “I thought it was thunder.” Another man said, “It was a big explosion cause it shook the building.”

Emergency management officials initially asked people to shelter in place due to the lage smoke plume but gave the all-clear a few hours later.

Air samples are being tested in the area, but so far, there are no reports of any immediate danger. This is the second fire at the refinery this month. Gas futures are already up because of this massive explosion.

For the latest details on this developing story, visit CBS Philadelphia at this link.