XINING, July 15 -- One person was slightly injured in an explosion that rocked a parking lot of Caojiapu Airport of Xining, capital of northwest China's Qinghai Province, on Tuesday afternoon.

The victim is a cleaner, who has been sent to hospital, said Ma Yanqing, head of the airport's operation and management department.

"The operation of the airport is normal now. No flights or passengers have been affected," Ma told Xinhua.

The official declined to comment on if the explosion was a terrorist attack, but he said the provincial public security department will publicize the result of their investigation once it's completed.

The parking lot is opposite terminal two of the airport and some 40 meters from the building.

The site has been cordoned off by police, who are investigating the blast. The parking lot has been emptied of vehicles, Ma said.

He said the explosion was caused by "unknown objects" and that police have taken samples for examination.

Witnesses said the explosives were settled in a garbage bin at a corner of the parking lot. Cleaners were around when the blast happened.

Caojiapu Airport is 28 km from downtown Xining. It was built in 1991 as an important transportation hub on the Qinghai-Tibet Plateau. The airport handled more than three million passengers in 2013.