SHANGHAI, May 22 (Xinhua) -- Shanghai customs authorities said on Sunday that they have busted a cigarette smuggling operation with the arrest of 20 suspects, six of whom were airport ground staff that helped the gang bypass customs checks.

About 4,000 boxes of foreign brand cigarettes were confiscated in the operation.

Local customs officials noticed a smuggling ring which had been transporting cigarettes from Japan to Shanghai recently.

On the night of April 21, four suspects arrived at Shanghai Pudong International Airport and bypassed customs checks with the help of ground personnel of the airlines. The four were caught in the airport parking lot with about 800 boxes of cigarettes, according to Shanghai customs.

The rest of the gang were caught the same night.

Nine of the alleged smugglers traveled between Osaka and Shanghai three or four times in a single week. The ring also included drivers and deliverymen.

The cigarettes have been mostly sent to Liaoning Province. The case is under further investigation.