Chinese officials on Wednesday warned that an extended low-flow period, caused by the lingering spring drought in central China, might pose a threat to navigation in parts of the Yangtze River, the longest waterway in China.

Boats are seen stranding on crackled bed of the Xieshan water area of the Poyang Lake in east China's Jiangxi Province, May 4, 2011. [Xinhua]

The persistent drought has reduced water levels in the middle of the river to a "worrying level," driving up the danger of ships grounding, said Wang Xiandeng, head of the Changjiang (Yangtze River) Wuhan Waterway Bureau.

Statistics indicate that the water level near Hankou of Wuhan, the provincial capital of Hubei, on the middle reaches of the Yangtze River, was measured at 2.87 meters on Wednesday, which was 3.26 meters lower than one year earlier.

To guarantee the safety of ships plying the river, dredging work was expected to ramp up, and more rescue vehicles may be put into operation this year, said Wang.

A drought hit central and southern parts of China after spring, drying up many rivers and reservoirs and causing problems for river traffic in some areas.

In the northern part of Zhejiang Province, which is located in east China, a record low rainfall ended in a traffic gridlock involving more than 700 ships on the Dongtiao Creek starting Saturday.

Efforts were organized to relieve the traffic jam, which was expected to clear by Friday.