YOKOHAMA, JAPAN - The man accused of murdering 19 disabled people at a Japanese care home in one of the country's worst ever mass killings pleaded not guilty Wednesday to the horrifying attack as his trial began.

Satoshi Uematsu, a former employee of the care center outside Tokyo, did not dispute his involvement in the horrifying stabbing rampage during his first court appearance on charges including murder.

After prosecutors read out the details of the charges, the judge asked Uematsu "is there anything in the charges that differs from the facts?"

"No there isn't," Uematsu replied, dressed in a navy suit with a white shirt and tie, his long black hair tied back in a ponytail.

But despite admitting the attack, Uematsu's lawyers entered a plea of not guilty, saying their client was suffering a "mental disorder" linked to his use of marijuana.

"He abused marijuana and suffered from mental illness. He became a different person and as a result, this incident happened," his lawyer said.

"He was in a condition in which either he had no capacity to take responsibility or such a capacity was significantly weakened."

The session was disrupted shortly after it began when court security restrained Uematsu after he reportedly attempted to put something in his mouth.

The disturbance prompted the judge to call an unscheduled recess, and Uematsu was not in court when the session briefly resumed in the afternoon.

Uematsu has reportedly said he wanted to eradicate all disabled people in the horrifying attack at the Tsukui Yamayuri-en center in the town of Sagamihara outside Tokyo, which also injured 26 people.

He turned himself in to police after the attack, carrying bloodied knives, and it later emerged that he had left his job at the home just months earlier and had been forcibly hospitalized after telling colleagues he intended to kill disabled people at the center.

He had been discharged after 12 days when a doctor decided he was not a threat. He had also written a letter outlining plans to attack the home, claiming "disabled people only create unhappiness."

Prosecutors said they would prove he was capable of taking responsibility for the attack, adding the rampage was "inhumane" and left "no room for leniency."

Uematsu faces the death penalty if convicted on some of the six charges, including murder, with a verdict expected on March 16. -AFP