An ice run has begun in the middle reaches of the Yellow River near Baotou City in north China's Inner Mongolia Autonomous Region, said the local meteorological station Friday.

An ice run usually takes place at the start of winter or spring when sections of the river freeze and then float down stream, said experts with the city's meteorological station.

At the start of winter, water from the upper reaches might hit ice downstream. In spring, an ice run moving downstream might crash into a frozen section of the river. Both scenarios can block the river, cause water levels to rise and cause flooding and dam bursts, experts said.

The middle reaches of the river were estimated to be free flowing by March 25, they said.

The 5,464-km Yellow River, the country's second longest, has its source in the northwestern Qinghai Province and flows through Sichuan, Gansu, Ningxia, Inner Mongolia, Shanxi, Shaanxi, Henan and Shangdong before emptying into the Bohai Sea.