An explosion at a check-in area of Shanghai's main international airport injured four people but did not cause any disruption to flights.

The small blast at Pudong International Airport, China's second-busiest, occurred at around 2.20pm local time on Sunday.

It appeared to have been caused by some sort of home-made explosive, the airport's management said on its verified microblog account.

It said the four injured people were taken to a hospital but gave no word about their condition.

There was no disruption to flights into or out of the airport, although police and internal security troops cordoned off the area and checked for additional explosives.

Ni Bowen, who was waiting to check into his Philippine Airlines flight when the explosion happened, said passengers ran for safety after a loud bang rocked the hall.

"At that moment, a beer bottle filled with white smoke rolled right by my feet. I was scared and made off at once," said Ni, 30, who works for a machinery manufacturer.

One of the injured, a Chinese man, sustained a severe neck injury which may have been self-inflicted.

Also injured was a 53-year-old Philippine man. The two others who were hurt were Chinese, including a 67-year-old man and 64-year-old woman who suffered injuries to their heads, hands and legs.

Pudong airport serves international flights but is also a hub for two major domestic airlines.