A 39-year-old man was arrested on suspicion of murdering his girlfriend's four-year-old son in a house in Kampung Sungai Udang here Sunday.

Klang Selatan police chief ACP Azman Abdul Razak said the man was picked up at his home near the scene at 7.10 pm, along with a 29-year-old woman, believed to be his sister-in-law.

Azman said the boy's body, which was wrapped in a towel, was found in an unused toilet in the house.

"Initial investigation found cuts and bruises on the boy's head and blood stain on his mouth and nose.

"Police also found a blood-smeared white towel, a cane and a PVC pipe believed to have been used to beat and abuse the victim," he told reporters at the scene.

Azman said police received a report from the suspect's neighbour who claimed that the suspect had asked for his help to dispose off the body of the child, who was believed to have died Saturday.

"Fifteen witnesses in the house will be called to facilitate further investigation into the case," he said.

The body was taken to Tengku Ampuan Rahimah Hospital for post mortem.