China is investing millions of dollars in a flood control project to prevent Mogao Grottoes, a UNESCO World Heritage Site in northwest China's Gansu Province, from seasonal flooding, the caves' administration said on Tuesday.

Designed to combat a once-in-300-year flood, the banks of the Daquan River where the grottoes are located, will be strengthened with concrete and steel bars, according to the Dunhuang Academy, which administers the 1,600-year-old caves.

The project was approved by the State Administration of Cultural Heritage with a planned investment of 20 million yuan (3.23 million U.S. dollars).

Half of the construction is complete, and the whole project is scheduled to be finished by November, sources said.

The Mogao Grottoes are known for their huge collection of Buddhist artworks -- more than 2,000 colored sculptures and 45,000 square meters of fresco paintings in 735 caves carved along a cliff by ancient worshippers. It became China's first UNESCO World Heritage Site in 1987.

Although located in desert areas southeast of Dunhuang City, Mogao Grottoes have been affected by flooding several times, and some lower-level caves have been damaged.

In June 2012, two flood-prevention dams near the caves were damaged and nearby open squares were also flooded. The caves were not inundated though.