The Beijing News newspaper said on its website the attack occurred aboard a public bus in Longyan in the coastal province of Fujian, south of Shanghai.
The newspaper and other reports gave no details of the attacker's identity or motive.
A brief video clip on the Beijing News website showed a half dozen police officers wrestling the attacker to the ground in the middle of a street as traffic flowed past.
In late November a car rammed into a group of children crossing a street in front of an elementary school in northeast China's Liaoning province, killing five people and injuring another 18.
Earlier that month, about 15 people died when a bus plunged off a bridge in southwest Chongqing municipality, after the driver got into a fist fight with a passenger who had missed her bus stop.
In February, a van packed with pressurized gas tanks and petrol-filled bottles caught fire and ploughed into pedestrians in Shanghai, leaving at least 18 people injured.
Grisly car accidents are common in China, where transportation authorities have struggled to enforce safety regulations, which are often flouted or go unenforced.