Eight blasts were heard but a search by a bomb squad turned up no other devices, China's state-run news agency Xinhua reported.
Police in Taiyuan, the capital of Shanxi province, said ball bearings and circuit boards found scattered at the scene indicated homemade bombs were used.
Police haven't publicly identified potential suspects, The New York Times reported. Shanxi's Public Security Bureau said it was conducting an "all-out investigation."
The explosions occurred three days before the Chinese Communist Party's Central Committee was scheduled to conduct its third plenum, during which China's economic course for the next decade is set.
On Oct. 28, a sport utility vehicle plowed through a crowd of pedestrians then caught fire at the entrance to the Forbidden City in Beijing, killing five people, including the vehicle's three passengers, and injuring 40. Chinese officials said the attack was carried out by ethnic Uighur extremists from the Xinjiang region.