The incident occurred in the southwestern Chinese city of Panzhihua, Sichuan Province, local authorities said.
The city's Communist Party chief Zhang Yan and mayor Li Jianqin were injured around 11 am when they were participating in a meeting at a local conference and exhibition center, Xinhua news agency reported.
They have no life threatening injuries, officials of the information department of Panzhihua city said.
Zhang, the party secretary, has worked in Panzhihua since 2006, and the mayor, Li, has worked there since last year, according to Chinese news reports. Both officials went to meetings and inspection visits with Chen previously, but there was nothing in the earlier reports to suggest trouble brewing.
Photos on Chinese news websites showed armored vehicles and paramilitary troops massed outside the exhibition center in the aftermath of the violence.