BEIJING -- China's postal service suspended mailing liquid parcels, mails containing liquid and a few other materials from June 1 to October 31.

The ban was part of the efforts to tighten security ahead of and during the Beijing Olympic Games, said a spokesman of the State Post Bureau.

During that period, all kinds of chemical products, powder goods, unidentified metal, mechanical and electrical products, sealed containers with unidentified gas or liquid are also banned from delivery.

People who have a necessity to mail parcels with the listed items will be asked to produce a safety certificate from local public security authorities.

Early last month, Beijing postal bureau said they would beef up inspections of parcels being sent to other Olympics host cities, including Shenyang, Tianjin, Qingdao, Shanghai and Qinhuangdao.

In mid-April, the Chinese aviation authority also instituted a liquid ban for carry-on baggage on domestic flights to ensure safety.