The attacker struck in the morning as students arrived for classes, mingling with parents at the school gates before suddenly pulling out his knife and slashing children, according to witnesses interviewed on local television.
In the aftermath, doctors treated small children and bodies lay covered in bloody sheets after the attack at Nanping City Experimental Elementary School in Fujian province. Police officers manned a cordon around the school. Some comforted distraught parents.
China has witnessed a series of school attacks in recent years, most blamed on people with personal grudges or suffering from mental illness, leading to calls for improved security.
The rampage in Nanping was finally stopped by passers-by and school security guards and the attacker was arrested, the reports said. The suspect was identified as Zheng Minsheng, 41.
Zheng worked as a senior nurse in a community clinic before resigning last June, the official Xinhua News Agency said, citing Huang Zhongping, spokesman for the Nanping city public security bureau.
Zheng was known to have a history of mental illness, said a man surnamed Wu in the Nanping city government office, who would not give his full name as is common among Chinese officials.
An unidentified former co-worker interviewed on Fujian television said Zheng was "difficult to get along with."
Eight children were killed, and five were being treated at a hospital, Wu said. Six died at the scene, which was smeared with blood from the sidewalk to the floor of an inner reception room.
The victims' ages were not immediately known, but Chinese elementary schools typically have students ages 6 to 12.
The school was closed and students were sent home for the day. Counseling will be provided for students when classes resume Wednesday, Xinhua said.
Recent school attacks include a July 2007 assault in which a mentally ill man wielding a wrench wounded 18 children and a teacher in a kindergarten in southern China before fleeing on a motorcycle and trying to stab himself to death.
In June the same year, a man slashed four students, wounding one seriously, in a high school in the southeastern city of Fuzhou, while elsewhere, police shot dead a suspected mentally ill man who threatened to blow up a school in southern China with dynamite.
China's worst such incident in March 2001 destroyed a schoolhouse and killed at least 42 people, most of them children. Officials blamed a mentally ill man who charged into the school in Jiangxi province with a bag full of dynamite. Parents disputed that, claiming their children had been forced to make fireworks at the school.