Authorities on Tuesday ordered the operators of a major reservoir at risk of overflowing, amid torrential rains in east China, to start discharging water from it. The Xin\'anjiang Reservoir, built on the upper reaches of the Qiantang River, opened three of its nine floodgates at about 9:30 a.m. Tuesday, said officials with flood control and drought relief headquarters of Zhejiang Province. The reservoir, built in 1959, has a maximum water-holding capacity of 21.6 billion cubic meters. But the water level had risen to 107.18 meters, or 0.68 meters above the warning line by Monday night. It may take 30 to 40 hours before the water level falls below 106.7 meters, officials said. The operator of the reservoir, the largest in eastern China, had not been forced to discharge water from it since 1999. Rain-triggered floods, the worst since 1955, have hit 10 cities of Zhejiang since last Saturday. More than 4.41 million local residents have been affected. Dikes near the city of Lanxi City were reported to have come close to overflowing due to surging water levels of the Lanjiang River, a tributary of the Qiantang River. The Xin\'anjiang Reservoir is located at the upstream of Lanjiang River but flood control officials say the release of water will not wreck havoc at downstream as the water level of Lanjiang has receded to about one meter below the warning line. In 1999, when the reservoir discharged water, eight floodgates were opened, almost inundating the downstream city of Jiande. \"This time, the impact is much smaller, and people living along the river bank won\'t be affected,\" said Hu Yaowen, deputy head of the provincial flood control and drought relief headquarters. Hu said the water flow downstream is estimated to rise to 8,000 cubic meters per second but is weaker than the flow at the flood\'s peak over the weekend, which was about 11,000 cubic meters per second. \"When the peak passed, it was peaceful, so we presume it will also be fine this time,\" Hu said. The Xin\'anjiang Reservoir is part of a tourist attraction dubbed \"Thousand Island Lake.\" Authorities have cordoned off the area to prevent tourists who usually venture into the reservoir area from being swept away by the torrents. Rain-triggered floods have swept large swaths of east and south China since early this month, leaving 175 dead and 86 missing so far, the Ministry of Civil Affairs said Monday.