WUHAN, July 30 (Xinhua) -- The Three Gorges Dam is preparing to control the biggest flood crest from the upper Yangtze River this year to protect the middle and lower reaches as central China's Hubei province goes on high flood alert.

The Three Gorges Reservoir began to release floodwater Monday noon at 48,000 cubic meters per second. The water inflow into the reservoir measured 51,000 cubic meters per second at 8:00 a.m. due to continuous rain in the upper reaches.

The inflow would reach 56,700 cubic meters per second, the peak of the floodwater, at 8:00 a.m. Tuesday, according to China Three Gorges Corporation, the builder of the gigantic Three Gorges hydropower project.

"The Three Gorges Dam has opened 18 sluices and the water level in the reservoir will continue to rise," said a worker with one of the dam's operation department. "The safety of the dam will be tested."

The two-way traffic at the Three Gorges ship lock was halted at8:00 a.m. Monday due to the floodwater.

Hubei Province, where the Three Gorges project is located, is also on high alert.

Water levels in the 1,392-km section of the river from Yichang to Hankou would exceed levels requiring the start of flood prevention work, according to the Hubei flood control and drought relief headquarters.

Water levels in certain sections would reach or exceed warning levels, the headquarters said.

The province had ordered a round-the-clock monitoring of the levees, said Liu Youfan, vice governor of Hubei.