Updated 05/15/11 – 4:29 p.m.

AURORA (CBS) — Six people, including three children, were killed in an apartment fire on the near east side of Aurora early Sunday.

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Firefighters were called to a fire just after 4 a.m. at a three-story stucco apartment building in the 700 block of Claim Street.

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The building was fully engulfed in flames when firefighters arrived, Aurora spokesman Dan Ferrelli said.

Fire happened at the second and third floor of the building, according to Aurora fire officials.

A witness, Rubin Delanora, told Newsradio 780 that he heard a woman from the building screaming “help me, help me, my chidren, my children.”

“I first saw a lot of smoke coming out of the windows,” he said. “I saw people in the street and coming from the building.”

Three young boys were among the six killed. Twelve more residents of the apartment were injured, at least two of them critically.

Among the injured was a 14-year-old boy who was the sole survivor of a family that perished in the fire, a relative’s boyfriend told CBS 2’s Mai Martinez. The teen is doing OK at Copley Hospital and knows the sad news about his family.

One boy, believed to be about 6 years old, was pronounced dead at Provena Mercy Medical Center in Aurora, officials said. An 8-year-old boy and a man between 30 and 40 were pronounced dead at Rush Copley Medical Center in Aurora. A 9-year-old boy and two women in their 30s were also pronounced dead at the scene.

As CBS 2’s Vince Gerasole reports, for the families of the dead and injured, coming to terms with the early morning fire was numbing.

Alicia Velisquez, speaking in Spanish and through an interpreter, said she lost her nephew, his wife and two of their three young sons, when a roaring blaze raced through the three-story apartment building as most of the 35 people inside were asleep.

“It’s something that I don’t wish upon anyone. It’s something that you just get in shock, it hurts, and you just don’t know what’s going on around you,” Velisquez said.

Jose Garcia, a cousin of one of the victims, said, “It’s very sad for our family.”

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“It’s an I credibly difficult day,” Ferrelli said.

The fire appeared to start in a first floor apartment. An open door to a stairwell acted like a chimney and vented deadly smoke and flames throughout the building.

“That created a chimney effect, which intensified the fire and smoke that was going throughout the building,” Ferrelli said. “There were several people seen running from the building.”

The fire traveled so quickly that those on upper floors jumped from windows to safety, because it was their only way out.

Survivor Pascal Vasquez said he had to slide down a telephone cable to get to safety.

As shocked survivors took refuge in a nearby church, neighbors came by with donated clothes to try and help.

“You don’t even have to know people to be upset,” neighbor Connie Cepeda said. “This is our neighborhood.”

The exact cause of the fire has not yet been determined. Authorities said the fire doesn’t appear to be suspicious in nature, but they have called in state and federal investigators because of the magnitude of death and destruction.

“Naturally, you don’t want to get tunnel vision when you go into a situation like this, and it’s way too early to rule anything out,” Ferrelli said.

In addition to those killed, four others, including a girl about 2 who was later airlifted to Loyola Medical Center, were also injured and transported to Mercy Medical Center, according to Ferrelli.

Two other victims were treated and released from Delnor Community Hospital in Geneva.

Six other people were also taken to Rush-Copley Medical Center. Ages and genders on the injured were not immediately known.

As of early Sunday afternoon, it was not known what started the blaze, but fire investigators have ruled out foul play, according to Aurora spokesman Dan Ferrelli.

Working smoke detectors were found in the common areas of the building.

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(The Sun-Times Media Wire contributed to this report.)