An anonymously written letter led Michigan inspectors to find the badly decomposed remains of 11 infants hidden in a ceiling compartment of a shuttered Detroit funeral home, police have said.

Inspectors found the remains at the former Cantrell Funeral Home, just hours after receiving the letter telling them where the bodies were located, Detroit Police Lieutenant Brian Bowser said.

They found nine bodies inside a box and two inside a casket.

The funeral home has been closed since April, when state inspectors suspended its license following the discovery of bodies covered with what appeared to be mould.

State regulators found "deplorable, unsanitary conditions" at the same premises, including embalmed bodies in an unrefrigerated garage and other badly decomposed remains, the Michigan Department of Licensing and Regulatory Affairs said in a statement at the time.

The remains of the infants, some of them apparently stillborn, were in a false ceiling between the first and second floors, Lieutenant Brower said.

Authorities do not know how long the remains had been stored there, he said.

Investigators also have not determined who might have left the bodies there.

"Obviously, it was either an employee or someone who had knowledge" of the funeral home and the building, Lieutenant Bowser said.

He also noted that the remains "were kind of hidden away".

Investigators have names for some of the remains and officials were contacting relatives, Lieutenant Bowser said.

Jameca LaJoyce Boone, the funeral home's designated manager for a year before its closure, said she was shocked by the discovery of bodies in the ceiling.

"I didn't know anything about that," Ms Boone told The Detroit News.

"I really don't know how that could even have happened."

AP/Reuters