What began as a case of a missing person led Japanese police yesterday to the arrest of a 27-year-old man after the gruesome discovery of nine dismembered bodies and their severed heads in his apartment.

Takahiro Shiraishi has confessed to murdering eight women and one man, and the police are treating him as a serial killer. The body parts were found in Shiraishi's two-storey apartment in Zama city in Kanagawa prefecture, to the south-west of Tokyo.

Local media quoted him as having told the police that he cut up his victims and "disposed of their flesh and internal organs like trash", while keeping their heads and bones, including arms and legs.

The police had been investigating the disappearance of a 23-year-old woman from Tokyo's Hachioji suburb, whose brother lodged a report last Tuesday after she went offline.

The woman, who had been seeking help for a mental disorder, had posted on Twitter that she wanted to commit suicide but was afraid of dying alone and was seeking a companion to do so.

That tweet was her first point of contact with Shiraishi, who the police believe used social media to lure victims who had publicly expressed their intention to kill themselves.

The rash of murders began around Aug 22, when the unemployed Shiraishi moved alone into the two-storey apartment in a quiet neighbourhood.

Local media reports said that Shiraishi was desperate to move into his own home immediately, even though it would have been cheaper had he moved in at the start of the following month.

"I dismembered the bodies in the bathroom," he was quoted by local media as telling the police.

"There is no doubt at all that I committed murder, and I cut them up with the intent to conceal and destroy evidence."

After the corpses were mutilated, Shiraishi allegedly covered them in cat litter and hid them in three cooler boxes and five large cold-storage containers.

Two severed heads were discovered on Monday, kept chilled in an ice box near the entrance to his apartment. The remaining heads and body parts were found in coolers and containers elsewhere in the apartment yesterday, according to local media.

The police have recovered a saw, which is believed to have been used to slice up the bodies, in Shiraishi's bathroom.

The suspect was tracked down by security camera footage which showed him with the missing woman near Hachioji station, and then at the Sobudaimae station near his home last Monday.

Residents who live in the vicinity told the media that while they had noticed a foul stench emitting from the apartment since late August, they had otherwise not seen nor heard anything amiss.

Police are now working to identify the other victims.

Mass murders are rare in Japan, although violent crimes by disillusioned youth periodically make the headlines.

In July last year, 19 people at a home for those with disabilities were killed and another 26 injured when former employee Satoshi Uematsu, 27, went on a stabbing rampage in the deadliest mass murder in post-war Japan.

In 2008, a 26-year-old man rammed a truck into the Akihabara electronics district before alighting and stabbing several others, killing seven people in all.