Downpours and water discharge from a reservoir along a China-Russia border river has submerged 90 percent of China's part of an island shared by the two countries, local border control authorities said on Sunday.

The entrance to Heixiazi Island has been closed by border control police of Jiamusi, Northeast China's Heilongjiang province, as most of the wet land and trees have been submerged, with only a few buildings seen above water level.

All construction projects on the island have been suspended, and more than 300 workers have been evacuated.

China and Russia ended a century-long dispute over the island in 2008, declaring each side owned half of the 335-square-km piece of land, which is found where the Heilongjiang River, known as the Amur River in Russia, and the Ussuri River meet.

Officials with the flood control and drought relief headquarters of Heilongjiang province predicted that the island might be fully submerged on Wednesday.

Heavy rain has hit the area since July, leaving floodwater from tributaries to flow into Heilongjiang River. The reservoir along the Zeya River, a major tributary of Heilongjiang River in the Russian territory, has discharged floodwater, putting more pressure on flood control in the lower reaches, said the authorities.

About 200 cars and 500 rescuers go to the island every day for flood control. Tourists have been warned not to visit the island.