At least four passengers were injured in an explosion that rocked check-in counters at Terminal 2 (T2) of Shanghai Pudong International Airport on Sunday afternoon.

The blast happened at 2:20 p.m. when "suspected homemade explosive material" exploded at the "C" check-in area at the airport's Terminal 2, the Shanghai Airport Authority said on its official Weibo account.

The victims have been rushed to hospital, the authority said.

The site has been cordoned off by police, who are investigating the blast.

"The operation of the airport is normal now. No flights have been affected," the airport added.

Witnesses said an object, which looked like a firecracker, exploded in the hand of a male passenger as he queued up in front of the check-in counter. He was among the injured and was seen lying on the ground after the explosion.

There were two luggage items had exploded within five 5 seconds after the first one went off, authorities said.

Local newspaper Xinmin.cn 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.

One of the four injured passengers was seriously hurt, Xinmin.cn said.

A video posted on Sina.com shows a plume of smoke rising from the airport counters.