Six ships passed through the northern track of the Three Gorges Dam lock on Tuesday. Their passage marks the reopening of the dual-track lock one month ahead of schedule.

Authorities say the cost of transport from the Three Gorges to Chongqing Municipality will be reduced by 40 percent.

The Yangtze River Administration of Navigational Affairs estimates the annual shipping capacity of the lock will double from last year's level to 100 million tons. The administration says the Yangtze River has surpassed the Mississippi and the Rhine to become the world's busiest river.

There has been an alternating one-way traffic restriction at the Three Gorges' lock since last September, as work began to raise the beds of the two uppermost levels. Traffic along the southern track resumed in January.