TOKYO -- Two children were killed and one injured when an unidentified man stabbed the children in a house on Japan's northern island of Hokkaido, Reuters quoted public broadcaster NHK as saying on Wednesday.

The attacker had turned himself into police, television said.

"A bald man in black clothing suddenly walked in, told me to be quiet and started stabbing," NHK quoted six-year Kazumi Kikuchi, now in serious condition with knife wounds, as telling her grandmother.

The incident comes almost exactly a month after Japan was stunned when eight Japanese elementary school children were killed by a former janitor with a history of mental illness, who walked into their school and went on a stabbing spree.

"The incident took place inside a house in a residential area," a police spokesman said.

NHK said Kazumi's two-year-old-brother Testuya and five-year-sister Masami had been killed in the latest attack in the town of Hiroo in southern Hokkaido, about 900 km (560 miles) north of Tokyo.