A series of package bombs exploded on Wednesday in the southwest China city of Liuzhou, killing at least seven people and injuring 51, state media said.
The official Xinhua news agency said police had determined the blasts were a "criminal" act and identified the suspect as a 33-year-old local man surnamed Wei, but added the investigation was continuing.
Media images showed a collapsed building, smoke and streets strewn with rubble in Liuzhou in Guangxi region. Two people were missing, state radio said on its microblog.
Bombs were sent to 13 places ranging from hospitals and shopping malls to prisons and government offices, reports said, adding that a terrorist attack had been ruled out.
The Ministry of Public Security has sent a team of experts to help with the investigation, Xinhua said.
Guangxi sits on the border with Vietnam and has several ethnic minorities, but is generally peaceful.
Disaffected or mentally unstable Chinese people have set off explosions in public places in the past. Explosives are relatively easy to come by, as they are widely used in China's large mining industry.
Such "sudden incidents", as Chinese authorities refer to them, are sometimes seen as linked to a widening gap between rich and poor and anger at corruption or environmental problems.
Hundreds have died in recent years in China's far western region of Xinjiang, in violence blamed by the government on Islamist militants, but that unrest only occasionally spills over into other parts of the country.