Police in central China's Hunan Province have offered reward to find a man who had allegedly caused an explosion in a taxation office that left four dead and 19 injured.

Liu Zhuiheng, 51, from Hengyang City, had fled after setting off the explosion in a taxation office in Changsha, capital of Hunan Province on July 30.

An initial investigation shows the explosion was a planned attack, police said.

Local police have listed Liu as wanted and offered 100,000 yuan (14,706 U.S. dollars) to citizens who can provide clues.