German police have arrested a 19-year-old man suspected of killing a nine-year-old boy and posting pictures of the victim's body on the internet.

Officers arrested suspect Marcel Hesse after he called from a fast food stall and reported a fire in a nearby apartment, where police later found another male body.

Earlier information about two more bodies being found in the apartment was incorrect, a police spokesman said.

The suspect had been sought since the body of a child living next door to Marcel was found on Monday.

The killing shocked the industrial city of Herne, not least because police said the suspect had boasted about his actions online.

Authorities said Hesse had posted a photo and video of the murdered child online to boast about the killing.

North Rhine-Westphalia's top security official, Interior Minister Ralf Jaeger, said at the time that the images "left even the investigators stunned."

A large-scale manhunt was launched, with police using helicopters and sniffer dogs to search the area.