The string of explosions that rocked the city of Changchun in China's north-eastern Jilin province on Friday afternoon was caused by a 56-year-old cancer sufferer who was "pessimistic with life", according to the city's municipal public security bureau.

The authorities said the blasts were set off by a man from Jiangsu called Guo Moutao, after he murdered another man in a money-related dispute in the nearby city of Songyuan.

Guo was killed by one of the explosions and another person was injured.

"Investigations showed that the suspect, Guo Moutao, was suffering from cancer and pessimistic with life," Changchun authorities said in a statement carried by Xinhua news agency.

"After killing a man he had an economic dispute with in Songyuan city, he drove to Changchun city at noon on Jan 25 and detonated a car that was parked in the underground carpark of Wanda Plaza."

The underground explosion was followed by at least 17 other blasts at the condominium-cum-shopping mall, and eyewitness footage on China's Twitter-like service Weibo showed explosives being lobbed out of the window of an apartment on the 30th floor.

The videos were later taken down from the platform.

City officials said that following the blasts a taskforce of more than 200 elite police officers from the provincial, municipal, and district levels was organised to investigate the explosions.

"By extracting DNA from the unexploded ordnance left at the scene, comprehensive on-site investigations and cross-references with extracted video surveillance, it was concluded that the man who died on-site, Guo Moutao, was the suspect in this case," said the Changchun Municipal Public Security Bureau.