SHANGHAI • A man hurled homemade explosives at the main international airport in China's commercial hub of Shanghai yesterday, injuring four others, and then attempted suicide, the local government said.

The unidentified man removed one or more beer bottles with explosive materials from a backpack before throwing them near a check-in counter of Terminal Two at the Pudong International Airport, the Shanghai government said in a statement.

He then took out a knife and slashed his neck, it said, adding the man is now in critical condition and is being treated at hospital.

His motive was not described, Agence France-Presse reported.

The four people hurt were lightly injured by exploding glass, said the statement posted on the Shanghai government's official microblog.

The incident was under investigation and only the three flights in that ticketing area were affected.

The official Xinhua news agency had earlier said the blasts were caused by fireworks.

Xinhua said those injured included a man from the Philippines, as well as a 67-year-old man and a 64-year-old woman - both described as Chinese.

The Xinmin Evening News said the two explosions occured within five seconds of each other .

A Reuters reporter at the airport said police in explosion-resistant suits were searching luggage, but travellers could freely enter the building.

Images and videos of the incident were widely shared on social media.

Unverified photos on China's Weibo microblog showed a person on a gurney being wheeled away by medical attendants, Reuters reported.

Meanwhile, online video clips showed dense grey smoke rising to the ceiling of the terminal, and paramilitary security forces rushing into the building immediately after the incident. Others showed police keeping people back from the scene, and abandoned luggage littering the floor.

The Associated Press news agency quoted traveller Ni Bowen, who was waiting to check in to a Philippine Airlines flight when the incident happened, as saying a loud bang was heard before passengers were sent scrambling for cover.

"At that moment, a beer bottle filled with white smoke rolled right by my feet. I was scared and made off at once," the agency reported the 30-year-old as saying.

Explosives are relatively easy to obtain in China, home to the world's largest mining and fireworks industries.

The incident came as people returned home after a public holiday and just days before Thursday's opening of a Disney theme park in Shanghai.

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

In 2013, a wheelchair user detonated a homemade bomb at Beijing international airport in a protest at alleged police brutality. The man was 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.