Detectives in the US are investigating after a severed head and body parts were found inside an apartment in San Francisco's Sunset District.

Police confirmed the crime scene was reportedly the address of a person who was reported missing a week ago.

A member of the public reportedly told police they should go check out an apartment on the 1600 block of Great Highway in the Outer Sunset on Sunday evening.

When investigators arrived, a police source said they found a severed head inside a refrigerator in the apartment. Other body parts were also found, but it was unclear whether the other remains were also in the refrigerator.

Private investigator Jeff Kaplan told KPIX 5 that police found the body while investigating the disappearance of Catono R. Perez, who last talked to family members on April 10th. A missing persons case was filed on April 20, Mr Kaplan said.

The 41-year-old's last known address was the apartment where the body parts were found, Mr Kaplan said. The private detective was at the apartment when police made the discovery.

"We had asked them [police] to check it out," Mr Kaplan said.

"We needed access to his apartment, and we had reason to believe there was evidence in there."

Mr Kaplan said he is working on behalf of Perez's family to locate him and said he was present when police entered the building.

He would not elaborate on the discovery. Authorities have not formally identified the remains.

Previously, police said they were investigating the possibility that the case is related to a recent officer-involved-shooting in Daly City early Easter Sunday, but investigators said it would be premature to say that the cases were definitively related.

Source: 9News