BEIJING: Seven people were killed on Wednesday when 15 letter bombs exploded in southern China, state media reported, with blasts reported in more than ten locations including government offices.

Atleast 51 people were injured by the explosives apparently placed in express delivery packages, the official Xinhua news agency said of the blasts on the eve of China's national day holiday.

Police described the blasts, which injured 51 people on the eve of China's national day, as a “criminal case”, ruling out a “terrorist act”. They said a 33-year-old local suspect had been identified but gave no immediate motive and were seeking his arrest.

“Currently, public security organisations are sparing no efforts to carry out investigation work,” police sources added.

The explosions occurred in at least 13 locations in a rural county in China's Guangxi region, the Nanguo Morning News, a local newspaper, cited police as saying.

The blasts hit a hospital, markets, a shopping mall, prison, bus station and several government buildings in Liucheng county.

The blasts occurred at the seat of Liucheng county and the surrounding areas, Xinhua said.

Pictures online showed a building half-collapsed. Witnesses also saw damaged vehicles on the road, Xinhua said.

State broadcaster CCTV cited a local police chief as saying the blasts were caused by several different explosive devices, adding that “the case is understood to be a criminal one”.

“Initial investigation showed that explosives could be inside express delivery packages."

He did not name any suspects or offer any motive for the explosions.

In recent years, China has grappled with a spate of violent knife and bomb attacks targeting markets and train stations, particularly in the country's west.

Explosives are relatively easy to come by, as they find wide use in China's large mining industry.