North China's Inner Mongolia is on high alert against the most severe Yellow River flood threat caused by ice blockage in 40 years as the spring thaw began on Tuesday.

More than 70,000 people in the region have been organized for rescue and disaster relief efforts along the 720 kilometer frozen stretch of the Yellow River, China's second longest, said Zheng Chunmao, Inner Mongolia Autonomous Region's top flood prevention official.

The People's Liberation Army's air force and artillery troops have also joined the flood prevention operation. Blasting will be carried out if there are any big ice blockages on the river.

Sections of the river freeze and thaw at different times. When an ice run flows into a frozen section it can become blocked. If the blockage persists, water levels may rise and cause flooding and dam bursts, threatening lives and property. The ice-run phenomenon takes place at the start of winter and spring.

The river's ice flood was the heaviest in 40 years, Zheng said. The river's watercourse in the region is currently holding some 1.8 billion cubic meters of water, 50 percent more than in a normal year. Low-quality dams in certain sections worsened the situation.

Vice Minister of Water Resources E Jingping urged local leaders on Tuesday to "make the safety of residents' lives a top concern and brace for the flood threat in an active way" in an inspection tour to the region.

"The ice blockage prevention of the Yellow River has entered a critical period," said E, also State Flood Control and Drought Relief Headquarters secretary-general.

He demanded "relevant departments closely monitor the ice run situation and prepare enough materials" in case of a dam burst.

The senior water official urged a speed-up of treatment efforts to consolidate embankments and deepen the watercourse of the river's stretch in the region.

The Yellow River in Inner Mongolia began to melt on Tuesday after a full thawing of the upper stretch in neighboring Ningxia Hui Autonomous Region.

On Monday, the water began to be diverted at 50 cubic meters per second to the Hetao area in Inner Mongolia to relieve floodwater pressure.

To help ensure a smooth thaw, the upper Liujiaxia Reservoir in Gansu Province has reduced sluicing water flow from 400 cubic meters per second to 240 cubic meters per second.

The Inner Mongolia stretch is forecasted to be fully thawed by late March.

The 5,464 km Yellow River originates in Qinghai Province in the northwest and flows through Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Henan and Shandong before emptying into the Bohai Sea.

(Xinhua News Agency March 12, 2008)