Poyang Lake, known as the kidneys of China due to the role it plays in regulating the flow of the Yangtze river, normally swells in summer due to rain and retreats in winter. Last year, it also unexpectedly shrank due to drought.
Temperatures of 35 degrees Celsius and above continued to menace other parts of China.
Northwestern Xinjiang, where temperatures hit a record high 52.2 degrees Celsius on Sunday, remained blanketed in worse-than-usual heat while in neighbouring Gansu province, some areas suffered intense heat while others warned of floods and landslides.
Chinese officials have warned repeatedly that China is vulnerable to the impact of climate change due to its large population and unevenly distributed water supplies.
Videos shared on social media this week showed vehicles slowing to a crawl in the megacity of Chongqing in the southwest as traffic police gave directions boot-deep in water. In northern Shanxi province, vehicles laid half submerged, with some piled on top of each other.
To the east in Jiangsu province, a waterfall tumbled into a high-speed railway station in rain-drenched Wuxi city, according to social media clips.
As many as 150 cities get waterlogged each summer, despite efforts to improve drainage.
In July 2021, extreme rain in the central Henan city of Zhengzhou killed nearly 400 people, including 14 who drowned in a submerged subway line. More rain had fallen over three days than what the city gets in a year.
Heavy rainfall of up to 130mm is expected in parts of Hebei, Beijing and Tianjin until Saturday morning, the national weather bureau warned.