Southwest China's Chongqing Municipality, which is located along the upper reaches of the Yangtze River, was on Monday hit by the most severe flooding since the flood season started this year.

The third flood of the year in the Yangtze occurred on Sunday in its upper reaches after heavy rainfall, according to the Changjiang Water Resources Commission of the Ministry of Water Resources. The commission issued flood warnings for a stretch of the upper reaches of the river and the Three Gorges reservoir on Sunday.

At around 6 a.m. Monday, Cuntan hydrologic station in Chongqing saw water exceed the warning level for the first time since the beginning of the flood season this year.

Currently, the water level in downtown Chongqing has kept rising, and is expected to reach the highest level Monday night, said Ran Jinhong, an official with the municipal flood control and drought relief headquarters.

"We have made advance preparations for flood control to ensure the smooth passage of the flood," Ran said.

The municipal maritime authorities imposed temporary traffic controls on parts of the upper reaches of the Yangtze River on Sunday to ensure shipping safety.