A house fire killed three people Friday morning in Gary’s Midtown section, police said.

The Gary Fire Department responded around 11:15 a.m. to a fire on the 3500 block of West 20th Avenue. Inside, firefighters found three bodies, Cmdr. Jack Hamady said.

Gary police were then called to the scene around 11:30 a.m. The Lake County coroner’s office has not released the names of the deceased.

Multiple members of a family are believed to have lived in the 1 1/2 story Cape Cod house, he said. Around four children were in daycare or in school at the time of the fire and are safe, Hamady said.

The cause is still under investigation. Authorities described the area as an active scene hours later. Part of the ceiling collapsed during the fire, Hamady said.

The cause is still unknown, ATF Chicago spokeswoman Kimberly Nerheim said.

The U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, and the Indiana State Fire Marshal have joined the investigation with Gary fire and Gary police, Hamady said. The ATF will be the lead investigative agency because it can bring sniffer dogs and more resources to determine how the fire started, Hamady said.