The annual Qiantang River tidal bore, which is expected to be seen this year during the National Day holiday week, attracts tens of thousands of people from home and abroad. [Photo by Zheng Zulin/China Daily]

In addition, the presence of a submerged sandbar at the mouth of the river acts like a springboard for the tide, sending the crest of the bore higher.

Also, combined with the gravitational pull of the celestial bodies and the centrifugal force produced by the rotation of the Earth, tidal waves are created for the first five days and in the middle of every month according to the lunar calendar, which adds up to about 120 days a year.

Around the middle of the eighth month this year, based on the lunar calendar, the tidal force reached its peak, and the waves were as high as 5 meters, with a tidal range of up to 10 meters between the highest and the lowest points.

However, the most extraordinary sight can be expected from Oct 4 to 7 during the country's yearly National Day holiday week.

The Qiantang tide has been well documented since ancient times.