The first passenger vessels passed through the world's largest ship lock yesterday without a hitch.

A passenger ship sails into the fourth chamber of the permanent ship lock as a gate opens at the Three Gorges Dam in Yichang, Hubei Province, June 16, 2003. [Xinhua]

Priemier Wen Jiabao on Monday described as vital achievements the filling of Three Gorges reservoir and the successful trial navigation of the ship lock.

Thousands of constructors and officials witnessed the historic event. It was preceded last week by vessels in two test navigations that were not carrying passengers.

The director of the Three Gorges navigation bureau, Zhang Qingsong, said the two passenger ships passed through the lock in just over two and half hours. The process finished about 11:55 am.

According to a circular issued by the Ministry of Communications, yesterday's success marked the start of a 12 month-long navigational trial for the ship lock.

The gateway, an essential part of the gigantic Three Gorges Project, will enable vessels with a maximum capacity of 10,000 tons to pass and navigate upstream to Southwest China's Chongqing Municipality.

Communications Minister Zhang Chunxian said yesterday: "China is opening a critical valve, linking the economic artery of the nation's west with the east.''

The five-step ship lock has been wedged into hills on the northern bank of the Yangtze River.

Before the occasion, Yao Yusheng, the deputy general engineer of the Yangtze River Navigation Affairs Bureau, said: "This will be a milestone in the shipping history of the Yangtze River.''

"The favourable conditions for navigation in the wake of the increased water volume of the river will enable shipping teams to enlarge their business and carry more freight,'' said Yao.

Already, some officials are saying that the shipping industry needs more reform in order to improve the efficiency of the lock.

"The problem facing us is that there are too many small boats on the Yangtze River and more time is needed for anchoring before they pass the ship lock,'' said Fan Qixiang, director with the General Corporation of Three Gorges Project Development.