BEIJING - The State Post Bureau has suspended the business of 17 Chinese express delivery companies because they lacked operating permits, according to the bureau's official website.

"Customers should be vigilant when using express delivery services," the bureau said on its website on Friday, adding that the public should alert the bureau if any of these companies continues to trade illegally.

The ban came after the bureau inspected the express-delivery companies at the end of last year to regulate it. The companies are located in six provinces and autonomous regions.

Regional branches of some of China's major express-delivery companies are named, including Shanghai Yuantong Express (Logistics) Co Ltd, ZTO Express Service Co Ltd, and Shentong Express Co Ltd.

The nation's express-delivery industry has experienced rapid development during recent years, largely driven by the country's booming online shopping market, where transaction volumes more than doubled to 520 billion yuan ($79 billion) in 2010 from 253 billion yuan in 2009, according to the research company Analysys International.

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In 2010, the number of express deliveries in China totaled 2.3 billion, a rise of 26 percent from 2009, with revenues hitting 57.5 billion yuan, a year-on-year increase of 20 percent, according to figures from the State Post Bureau.

But such rapid development can lead to problems, analysts said. A common complaint among users is about extended delays in deliveries before long holidays because of the companies' increased volume of traffic, and because many employees have quit their jobs because of the arduous nature of the work and low pay.

A branch of Shentong Express in Shanghai which was found in December to employ an unsatisfactory method of sorting parcels has triggered dissatisfaction among users. The branch was later hit with a 60,000 yuan fine, and a four-week suspension of business.

The case underlined the fact that the industry lacks a standardized operating method and is over-reliant on human labor rather than machinery, analysts said.

Though the industry is expanding rapidly, it is still plagued with problems, such as the poor professionalism of staff members and a lack of information-based operational and management expertise, the analysts said.