A 480-kilometer-long ice run has appeared in the Yellow River, China's second longest waterway as of 10 a.m. Wednesday, said a report released by the Yellow River Conservancy Committee (YRCC) Thursday.

The ice run was sighted in the sector of the river running through north China's Inner Mongolia Autonomous Region. The run was caused by a suddenly sharp temperature drop, according to the report.

The lower reaches of the Yellow River saw the first ice run this winter on 8:00 a.m. Wednesday, two days earlier than the average from 1970 to 2005, according to the report.

An ice run usually happens at the start of winter or spring when a piece of water freezes and then dislodges and floats down stream, said experts with the YRCC.

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.

The YRCC has warned of possible dangers brought by the ice run. It has told local departments in provinces where the river runs through, to step up patrols along the riverside, watch the weather and ice flows closely so that efficient measures can be adopted in case of emergencies.

The 5,464-km Yellow River 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.