READING, Pa. -

Two people, including a firefighter, were injured in a fire that broke out in an apartment building in Reading overnight.

The call came in shortly before 4 a.m. Wednesday from the 100 block of North 9th Street.

The first firefighters to arrive on the scene found heavy fire on the top floor of the four-story building, said Todd Iaeger, Reading fire marshal.

The raging fire quickly went to three alarms, bringing in crews from the suburbs to help city firefighters get the upper hand.

"It all happened so fast. It was like small flames coming out the window and then huge flames, and I was like, 'Oh my God,'" said Yolanda Moultrey, who added that she barely had time to grab her son and get out of the burning building.

One woman was injured and transported to Reading Hospital before being transferred to another hospital. Officials on the scene did not know the nature of her injuries.

Preliminarily, investigators believe the fire may have started in her apartment and are waiting to talk to her and her adult son, who was reportedly at the apartment just before the fire.

A firefighter was also taken to the hospital for treatment of a minor injury. He has since been released, Iaeger said.

The Red Cross is assisting 13 adults and seven children who lived in the building's nine apartments, said Adrian Grieve, executive director of the Berks County chapter. A temporary shelter has been set up for them at the nearby YMCA on Washington Street.

Investigators have not yet determined what sparked the fire, but the federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) is assisting with the investigation, Iaeger said.

The magnitude of the fire made fire crews think about the two Philadelphia firefighters who were killed Monday in a fire that caused a building to collapse.

"We all knew the job when we signed up for it. Our deep-felt sympathies and our hearts go out to our brothers and sisters in Philadelphia right now," said Iaeger.

The Reading Fire Department said it plans to send a large contingent of firefighters to the funerals of the two Philadelphia firefighters.