Water flow rates through the upper reaches of the Yangtze River in central China's Hubei Province rose Monday, as already drenched riverside towns prepare for even more flooding.

The water flow rate into the Danjiangkou Reservoir from the Hanjiang River, the second largest branch of the Yangtze River, in northern Hubei Province, peaked at 34,100 cubic meters per second Sunday, the highest in almost three decades, the provincial disaster relief headquarters said.

The reservoir's water level is expected to rise to at least 155 meters on Tuesday, about 6 meters above the reservoir's danger level.

Authorities Monday said the flood-control situation along the Hanjiang River remains "very severe" and they have ordered the operation of a flood buffer system -- the diversion of water flows into an emergency reservoir capable of holding 1.6 billion cubic meters of water.

Water flow rates at the Three Gorges Dam, meanwhile, at another section of the upper Yangtze River, rose Monday after a three-day lull.

The water flow rate hit 40,500 cubic meters per second Monday morning, and it is expected to continue to rise until it peaks on Tuesday.

Engineers at the dam located in Yichang City, in central China's Hubei Province, said the water level at the Three Gorges reservoir behind the dam may exceed its year high level of 158.86 meters, which is 13.86 meters above the danger line.

Flooding has killed at least 13 people in Yichang in the past three days.

Zhao Yunfa, a senior engineer at the Three Gorges Dam project, said further rain in the already flooded area caused the resurgent flood-waters.

Last Tuesday, the flow on the Yangtze River's just above the Three Gorges reservoir topped 70,000 cubic meters per second, about 20,000 cubic meters per second more than during the 1998 floods that killed 4,150 people and the highest since the dam became fully operational in 2009.

Engineers said Monday's flow rate is unlikely to exceed last Tuesday's peak.

Floods in China this year had left 742 people dead and 367 missing as of last Friday.

Premier Wen Jiabao has urged local authorities to fully prepare for the "grave flood-control situation."