At least 19 people were feared dead and 45 injured after an attack by a knife-wielding man at a facility for the disabled in Japan early on Tuesday, national broadcaster NHK reported.
Police in Sagamihara, Kanagawa Prefecture, about 40 km southwest of Tokyo, have arrested Satoshi Uematsu, a 26-year-old former employee at the facility, Japanese media reported.
They said staff called police at 2:30 am local time (1730 GMT Monday) with reports of a man armed with a knife on the grounds of the Tsukui Yamayuri-En facility.
The 3-hectare facility, established by the local government and nestled on the wooded bank of the Sagami River, cares for people with a wide range of disabilities, NHK said, quoting an unidentified employee.
Media reports said the man, wearing a black T-shirt, did not have a knife when he turned himself in at a nearby police station. Police said they were still investigating possible motives.
Asahi Shimbun, a local newspaper, reported that the suspect was quoted by police as saying: "I want to get rid of the disabled from this world."
Fifteen people were confirmed dead while four were in cardiac arrest, the media reports said. The wounded were taken to at least six hospitals in the western Tokyo area.
Twenty-nine emergency squads responded to the attack, Kyodo news reported.
A man identified as the father of a patient in the facility told NHK he learned about the attack on the radio and had received no information from the center.
"I'm very worried but they won't let me in," he said, standing just outside a cordon of yellow crime-scene tape.
Kyodo, citing the facility's website, said the center had a maximum capacity of 150 people.
Such mass killings are rare in Japan.
A man went on a stabbing rampage in January 2008, killing seven people and wounding a dozen others in a crowded Tokyo shopping street.
The man, who said he was tired of life, drove a rental truck into a crowd of pedestrians at lunchtime. He then walked down the street knifing passers-by in Akihabara district, known for its discount electronics and maid cafes.
In another incident eight children were stabbed to death at their school by a former janitor in 2001.