SHANGHAI — A 29-year-old inveterate gambler has been identified as the lead suspect behind a small explosion at Shanghai’s main international airport that injured four people, city police said Monday.

A statement on the police force’s microblog said Zhou Xingbai had travelled to Shanghai from the neighbouring province of Jiangsu to commit the crime and had previously posted on the internet that he was deep in debt and intended to “do something really crazy.”

It said Sunday’s explosion was carried out using fireworks stuffed inside empty beer bottles.

The blast at a check-in area at Pudong International Airport, China’s second-busiest, occurred at around 2:20 p.m., but caused no disruptions to flights. Zhou was believed to have been among those taken to the hospital, possibly with a self-inflicted injury to the neck.

The police statement said Zhou was originally from the poor southern province of Guizhou but moved to the industrial east after graduating from high school in 2006 and worked at a series of factory jobs. It said he lost all his money gambling online and was forced to borrow from friends to survive.

In his online note, Zhou had said he was certain he would be killed while carrying out the attack.