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The tide is seen in Jiaxing on Sept 9. [Photo provided by Wang Zhijie]

Visitors gathered near Guanchao Park in Haining, a county-level city in Jiaxing, East China's Zhejiang province, to watch the annual "Ghost King Tide" of the Qiantang River on Sept 9. 

The tidal bore surged forward like galloping horses, creating a thunderous roar as waves struck the embankment.

Experts noted that the tide, with a head about 1.1 meters high resembling a massive water wall, occurs around the 18th day of the seventh month of the traditional Chinese calendar when the river enters its autumn flood season. Due to its fierce momentum and loud resonance, locals call it the "Ghost King Tide", which is as spectacular as the traditional bore seen in the eighth month of the traditional Chinese calendar.

The phenomenon results from a combination of celestial gravity, the Earth's rotation, and the river's trumpet-shaped estuary. During the mid-seventh month of the traditional Chinese calendar, the alignment of the moon, sun, and Earth, strengthened by southeast monsoons, pushes river water against the sea to create the tidal surge.

The tradition of tide watching along the Qiantang River dates back more than 2,000 years to the Han (206 BC-AD 220) and Wei (220-265) dynasties, reaching a peak during the Song Dynasty (960-1279). By the Southern Song Dynasty (1127-1279), Aug 18 was established as a festival for tide viewing, naval drills, and rituals.

Organized research began in 1957, with systematic measurements recorded from 1974 onward, and scientific study has continued for over six decades.