An explosion ripped through a fast-food restaurant in Heilongjiang province yesterday, but police were able to evacuate the premises after receiving a rare warning by phone.
Two police officers suffered burns in the blast but customers and staff of the Dicos restaurant in Anda city were evacuated in time and no civilian casualties were reported.
Police said the morning explosion was a suspected "revenge" act, without further elaboration. But analysts said such attacks were getting more sophisticated amid growing violence over various social grievances on the mainland.
Local authorities said police received a warning call four minutes before the explosion.
Police confirmed that an explosive device was left on the stairway leading to the first floor, and that they had an image of the suspect, China Central Television reported.
A man came into the restaurant, in the centre of the city, and left a bag inside, the Heilongjiang Morning Post reported, citing a witness. The man then alerted the restaurant by phone and a staff member called police, the newspaper said.
Li Wei, a Beijing-based anti-terror expert, said the explosion appeared to have been motivated by personal reasons. But unlike past patterns of social violence, the method was similar to terror attacks abroad.
"In the past, attackers only wanted to kill as many as possible," said Li, director of the anti-terrorism research centre at the China Institute of Contemporary International Relations.
"But now … [they] want as many people as possible to see what they are doing."
Zhou Xiaozheng, a professor of sociology at Renmin University of China, said attackers were becoming more sophisticated in creating an atmosphere of terror, instead of simply killing innocent people.
He questioned the "iron fist" approach often employed by the authorities in dealing with social unrest. "I believe the harder you crack down, the more terror there will be … there will be more and more such attacks in the future," he said in calling for more research into individual cases and finding ways to prevent them from occurring.
Last month, a man in Anhui who was reportedly denied a government low-income allowance carried out a suicide bomb attack at the village government office, also killing an official.
And just days before that, a 51-year-old former high-school teacher boarded a crowded bus in Yibin, Sichuan, and set it on fire, killing himself and wounding more than 70 people, including schoolchildren.
Yesterday's explosion came at a time that police around the country are on high alert after a series of terror attacks blamed by the authorities on separatists from Xinjiang.