Qinghai has a large ethnically Tibetan population and has been under tight security as Beijing tries to head off trouble during sensitive anniversaries, including of last year's anti-government riots in Lhasa.
But Li said the people involved in the rampage were not Tibetan. He said they were a married couple and four men who were mostly from Henan in central China.
Li said the group left the station after injuring two officers but returned later with 20 other people for a second attack. He said police had to deploy a tactical squad to stop the fighting.
The official Xinhua News Agency cited police as saying none of the attackers was injured.
Li said most of the second group of attackers left, but the original six were being held while an investigation was conducted.
Civilian attacks on the military and police are extremely rare in China, although at least two attacks were reported earlier this month. A bomb was thrown into a newly built and unoccupied police station in a Tibetan area in western China, while in the city of Chongqing, next to Sichuan province, an on-duty soldier was fatally shot by attackers who then stole his machine gun.
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