SHANGHAI (AFP) - A man hurled homemade explosives at the main international airport in China's commercial hub of Shanghai on Sunday (June 12) afternoon at about 2.20pm, injuring four others, and then attempted suicide, the local government said.

The unidentified man removed a beer bottle or bottles with explosive materials from a backpack before throwing it 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 at his neck, it said, adding the man is now in critical condition and is being treated at hospital. His motive was not described.

Four passengers were injured in the incident, said the statement posted on the Shanghai government's official microblog. The official Xinhua news agency said the 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.

Flights were not affected, the Shanghai Airport Authority said on its Weibo account

Xinhua news agency said the explosives were firecrackers.

A report on Sina.com said two luggage items had exploded with five seconds of each other. The luggage were then 15m apart, the report said.

It quoted a passenger identified only by her surname Xue as saying that she heard a man yelling "No!" and "Ah!" shortly before the blast as she was checking in for her flight to Thailand.

Passengers scrambled to run to safety as the explosion occurred, said Ms Xue. A video posted on Sina.com shows a plume of smoke rising from the airport counters.

Pudong Airport, which opened in 1999, is a major international aviation hub in China. It has two main terminals and serves some 60 million passengers a year.

Nervous Chinese were speculating on the cause of the blast even as investigations were underway, with many pointing to a possible terror attack.

The incident happened despite stepped up security at Chinese airports in the aftermath of the Brussels terror attacks in March.

There have been several cases in China of disgruntled individuals setting off explosions or starting fires in revenge for perceived wrongs, Agence France-Presse reported.

In 2013 a wheelchair-bound man from southern China detonated a homemade bomb at Beijing international airport in a protest at alleged police brutality, the report said.

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 others.