Nearly half the country's total area had now experienced temperatures of 35 degrees Celsius or more over the past month, China's weather agency says.
China has issued its first national drought alert of the year as authorities battle forest fires and mobilise specialist teams to protect crops from scorching temperatures across the Yangtze river basin.
The national 'yellow alert', issued late on Thursday, is two notches short of the most serious warning on Beijing's scale.
It comes after regions from Sichuan in the southwest to Shanghai in the Yangtze delta have experienced weeks of extreme heat, with government officials repeatedly citing global climate change as the cause.
In one of the Yangtze's important flood basins in central China's Jiangxi province, the Poyang Lake has now shrunk to a quarter of its normal size for this time of year, state news agency Xinhua said on Thursday.
The water resources ministry has instructed drought-hit agricultural regions to draw up rotas determining who can access supplies at any particular time, to ensure they do not run out.
According to data from China's emergency ministry late on Thursday, high temperatures in July alone caused direct economic losses of 2.73 billion yuan ($400 million), affecting 5.5 million people.
Extreme heat in Chongqing
China's National Meteorological Center (NMC) renewed its high-temperature red alert on Friday, the 30th consecutive day it has issued alerts, it said on its Weibo channel.
State forecasters also predicted that the current heatwave would only start to abate on August 26.
The weather agency said in its daily bulletin that 4.5 million square kilometres of national territory had now experienced temperatures of 35 degrees Celsius or more over the past month - nearly half the country's total area - with more than 200 weather stations recording record highs.
As many as 66 rivers across 34 counties in the southwestern region of Chongqing have dried up, state broadcaster CCTV said on Friday.
Rainfall in Chongqing this year is down 60 percent compared to the seasonal norm, and the soil in several districts is severely short of moisture, CCTV said, citing local government data.
The district of Beibei, north of Chongqing's urban centre, saw temperatures hit 45 degrees Celsius (113 degrees Fahrenheit) on Thursday, according to China's weather bureau.
Chongqing accounted for six of the 10 hottest locations in the country on Friday morning, with temperatures in the district of Bishan already approaching 39 degrees Celsius. Shanghai was already at 37 degrees.
The Chongqing region's infrastructure and emergency services have come under increasing strain, with firefighters on high alert as mountain and forest blazes erupted across the region. State media also reported an increase in cases of heatstroke.