ZHENGZHOU - A man with mental illness stabbed four of his family members to death on Wednesday morning in Central China's Henan province, local police said on Thursday.

The incident happened in Guangyang town of Fangcheng county, where the man is thought to have attacked his father, son, wife and nephew with a knife.

Neighbors said the killer returned to Henan on Monday from China's northern city of Tianjin, where he had worked, accompanied by his relatives.

Local government has launched an investigation into the case.