TOKYO (AP) _ A 17-year-old student allegedly beat his mother to death with a baseball bat after attacking four schoolmates in an argument reportedly over the length of his hair.

One of the students suffered a fractured skull and was being treated at a local hospital, said Okayama prefectural (state) police in western Japan. The three others were slightly injured on their legs and backs.

The four were attacked with a metal bat during baseball practice Wednesday. About an hour later, the boy's father found his wife at home on the floor and bleeding from the head, police said.

Kazuko Oka, 42, was taken to a hospital where she was confirmed dead. A blood-stained baseball bat was found near the body.

The attacks occurred in Oku-gun, about 350 miles, west of Tokyo.

About 80 policemen searched through the night for the attacker, but his whereabouts were not known Thursday morning, national broadcaster NHK television reported.

Kyodo News agency said the teen-ager had quarreled with the four teammates over the length of his hair. Police, however, said they were still investigating the alleged motive.

Japan, known as a relatively crime-free country, has been plagued recently by high-profile violence involving teen-agers.