SHANGHAI • Chinese police yesterday identified the suspect in a bombing at Shanghai's main international airport which injured four people as a 29-year-old man with heavy debts from online gambling.

Zhou Xingbai had been working at an electronics company in Kunshan city, near Shanghai, but had lost his savings through gambling and was having difficulty supporting himself, the Shanghai police department said in a statement on its official microblog.

Zhou told his friends through social media that he "owed many people money" and was "preparing to do something extremely crazy" and "losing his little life was a certainty", the statement said.

A previous government statement said Zhou threw a beer bottle packed with explosives near a check-in counter in Terminal 2 at Pudong International Airport on Sunday afternoon. He then took out a knife and slashed at his own neck before being admitted to hospital in critical condition.

Police said he used gunpowder from fireworks in his home-made explosive, residue of which was found in his rented room in Kunshan.

"A beer bottle with a burning fuse rolled into the queue when we were waiting to check-in," passenger Susan Shen was quoted as saying by the Shanghai Daily newspaper. "And then suddenly the bottle exploded with a loud bang and colourful flash like fireworks."

A nearby hospital took in the four casualties, who were slightly wounded by bottle fragments, police said. One of them was a Philippine citizen.

By late Sunday afternoon, the airport was calm. Twelve of the next 18 flights scheduled to land were listed as delayed for up to four hours.

The cavernous departure hall of Terminal 2 was operating across two-thirds of its length, but Aisle C, where the explosion occurred, was roped off and uniformed security personnel with black assault rifles slung over their shoulders stood guard, making it difficult to see any damage.

Zhou, originally from the southwestern province of Guizhou, had a high-school education and worked at various jobs before arriving in Kunshan in 2014, police said.

There have been several cases in China of disgruntled individuals setting off explosions or starting fires in revenge for perceived wrongs.

In 2013, a man who used a wheelchair detonated a home-made bomb at Beijing International Airport in protest against alleged police brutality. Ji Zhongxing was later sentenced to six years in jail.

Last year, an unemployed man set off an explosion at a public park in the eastern province of Shandong, killing himself and another person and wounding 24.

AGENCE FRANCE-PRESSE, NEW YORK TIMES