A white, Atlanta-area police officer shot dead a naked and unarmed black man acting erratically in his apartment complex and who was possibly suffering from a mental illness, the county police chief said.

A Dekalb County police officer responded to a caller who said a man was "acting deranged, knocking on doors, and crawling around on the ground naked," at around 1 p.m. Monday, Cedric Alexander told reporters.

The officer encountered the man, who was not wearing any clothes, in the parking lot, Alexander said at a conference published online by local broadcaster Fox5.