Over 100 masked men attacked a governmental security checkpoint in the town of Ejin, in the northern Chinese state region of Inner Mongolia at around 3am local time on Monday, state media said.
The attackers injured 13 people and destroyed 11 vehicles and the equipment in the office.
They used pepper spray against the staff, tied them up and threatened to beat them to death, according to the China News Service.
Six people were taken to the hospital for treatment.
Spokesman for the Ejin government said the attackers used two bulldozers for the attack and stole any property they could find.
Reports later said the attack was likely a result of a long running dispute over land rights in Ejin.
Ejin was a part of Gansu state until 1979, when it was made a subdivision of Inner Mongolia.
The town has a population of 32,000 people consisting of mostly farmers and herders.
Over the past few years, ethnic Mongol herders of Inner Mongolia have been complaining about mining and desertification destroying their grazing land.
Security measures are generally high in the region.