A teenage girl and her baby boy were killed in a South Side fire early this morning.

The deadly fire broke out around 4:45 a.m. in a two-story apartment building at 5307 S. Marshfield Ave., Chicago Fire Department spokesman Kevin McGregor said.

Gabrielle Green, 17, and her 7-month-old son, Omarion Green were both found dead inside the burning building.

Firefighters arrived at the fire four minutes after the first alarm and found the building already in flames. They were unable to reach the victims they knew were trapped inside, McGregor said.

Spokeswoman Eve Rodriguez said freezing temperatures made fire hydrants inaccessible, but firefighters were able to get enough water from their trucks, which are equipped with 500-gallon tanks.

"These hydrant issues absolutely did not hamper rescue efforts," Rodriguez said.

Because of suspicious evidence found at the scene and witness interviews, the fire department has turned the investigation over to the Chicago Police Bomb and Arson squad, McGregor said.

Chicago Police spokesman Wayne Frisbie said officials do not yet know the cause of the fire.