BEIJING (Reuters) - China's northern region of Inner Mongolia is on high alert against a severe flood threat caused by ice blocking the Yellow River during the spring thaw, state media said.

More than 70,000 people in the region were on standby for rescue and disaster relief efforts along the frozen 720-km (450-mile) stretch of China's second longest river, known as "China's sorrow" for its frequent flooding.

"The People's Liberation Army's air force and artillery troops have also joined the flood prevention operation," Xinhua news agency said. "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. If a blockage persists, water levels may rise and cause flooding and dam bursts, threatening lives and property. The ice-run phenomenon happens at the start of winter and spring.

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The river's ice flood was the heaviest in 40 years, Xinhua said.

"Low-quality dams in certain sections have worsened the situation," it said.

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

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.

In Qinghai, 14 Tibetan herdsmen, including a 9-day-old baby, were rescued on Tuesday after being trapped on a snow-covered mountain for 40 days, Xinhua said.

The herdsmen were well except for a 63-year-old who suffered snow blindness, according to rescuers. The baby and his mother were sent to hospital for observation.

(Reporting by Nick Macfie; Editing by Alex Richardson)