XINING, July 15 -- An explosion rocked a parking lot of Caojiapu Airport of Xining, capital of northwest China's Qinghai Province, at around 1:40 p.m. on Tuesday. No casualties have been reported yet.

The site has been cordoned off by police, who are investigating the blast, an airport member of staff told Xinhua.

The parking lot has been emptied of vehicles.

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

The operation of the airport has not been affected.

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.