Japanese news agency Kyodo reported that a knife-wielding man had attacked the Tsukui Yamayuri En facility in Sagamihara, Kanagawa Prefecture, early Tuesday (late Monday GMT) when most of the patients would have been sleeping.
A man is reported to have turned himself in to a local police station around 3 a.m. (1800GMT Monday) where he was promptly arrested on suspicion of murder.
Police have said that of the 25 injured, 20 are in a serious condition.
Reports say the man, who the facility identified as a former employee, has admitted to the attack with police quoting him saying “it’s better that the disabled disappear.”
The death toll, at 19, makes it the largest mass murder in modern Japanese history, even more than the infamous 1995 sarin nerve gas attack on the capital’s subway system which killed 12.
There have been two other serious attacks using knives (it is almost impossible to obtain a gun in Japan).
In June 2001, a man armed with a kitchen knife broke into an elementary school in Osaka and killed eight children.
In 2008, an assailant drove a truck into a crowd in Akihabara section of Tokyo, and then got out and stabbed others, totaling seven dead.