Firefighters and police responding to a blaze at a suburban Chicago house on Wednesday saw a man shoot himself in an apparent murder-suicide that left four people, including a 5-year-old boy, dead, authorities said.

The boy was found in the rubble of the fire Wednesday afternoon. The bodies of the suspect, another man and a woman were also recovered, officials said. It wasn't immediately clear if the boy was shot, but police said all of the adults had gunshot wounds.

All four people are related, but authorities wouldn't provide additional details. The victims were not immediately identified.

The fire started around 5 a.m., in the 1 1/2-story home in Oak Lawn, according to authorities, who said the house was nearly fully engulfed in flames when fire crews arrived.

"We encountered a vehicle in the garage and noises coming from the vehicle," said Oak Lawn Police Chief Michael Murray. "At that time we approached the vehicle and opened the door, and observed an adult male in the driver's seat take his own life with a shotgun."

Firefighters were hampered in battling the blaze because of frozen hydrants. The fire was put out after about four hours.

Officials have yet to say what sparked the fire. The South Suburban Major Crimes Task Force is investigating the deaths and fire.