At least two bodies were found inside the remains of an abandoned house that burned in northwest Alabama early Monday, authorities said.

Firefighters were called to a blaze around 4 a.m. and found the structure engulfed in flames, news outlets reported. Once the fire was under control, an inspector found the bodies in different parts of the house and was trying to determine if more people were present.

“The house is unstable and partially caved in, which has caused some challenges for our investigators to do their job fully,” said Florence Fire Chief Jeff Perkins.

Authorities were working to determine the identities of the people and the cause of death. There were indications that homeless people had taken shelter in the house, officials said.

The house didn’t have electrical service, and the cause of the fire was not immediately clear.