Six people, including four children, died in a fast-moving fire in a North Philadelphia row-house early Saturday.

Two women and four children, ranging in age from 2 to 12, died in the blaze on Sixth Street near Glenwood Avenue, fire officials said. The fire at the two-story house also spread to adjacent homes, but no other injuries were reported.

It took firefighters only three minutes to respond to the blaze around 5 a.m. but by the time they arrived, the house was engulfed in flames, Acting Fire Commissioner Lloyd Ayers said. The blaze was brought under control in about 20 minutes, he said.

Five of the people in the house died at the scene and the sixth victim, a young boy, died shortly after being rushed to Temple University Hospital (search), officials said.

The cause of the blaze was under investigation. Officials declined to comment about several neighbors' reports that they heard what sounded like gunshots and came outside to discover flames pouring from the house.

Investigators "are going to go through the place, they're going to look at every aspect of the home and they're going to ascertain what happened," Ayers said.

Homicide detectives joined investigators from the Fire Marshal's office, as is protocol when a fatal fire's cause cannot be immediately determined. However, authorities said it would likely take days before they could make any conclusions.

"The homicide unit is on the scene just to make sure preliminarily that we cover all the bases," police Capt. Richard Ross of the homicide unit said. "It's very early in the investigation so there are a lot of questions we need answered."

Neighbors said one of the women who died worked as a corrections officer and lived in the home with her grandchildren. The victims' names were not released pending notification of relatives.