Police said the incident occurred near a bus station in Ouhai District at 2pm on Tuesday when a man surnamed Dong rushed onto the road and blocked the vehicle of a female driver surnamed Du, Wenzhou City News reported.
The man then climbed on the car's hood and started hitting the windshield while Du screamed inside, police said.
Several minutes later, Du got out of the car to flee, but the man jumped on her and started gnawing on her face once they were on the ground, police said.
Passers-by said Du's face was covered in blood. They said they tried to pull Dong off the woman, but he seemed so "crazy" that they couldn't stop him.
Police stopped the man. Doctors at a nearby hospital said Du will need plastic surgery to repair the damage from the bites on her nose and lips.
Police said Dong had been drinking heavily with his friends at lunch that day.