A warning issued on Tuesday by the National Meteorological Center marked the 19th consecutive day of hot weather alerts, during which some eastern cities have seen record high temperatures.

The center also warned of the increased risk of heatstroke due to humidity. Health risk warnings are based on a five-level scale - in addition to the familiar four-level color codes for heat warnings. Health risks are now at the highest of the five levels in 12 provinces and municipalities in eastern and northwestern China, the center said.

It means residents in places such as Shanghai and the provinces of Zhejiang, Jiangsu, Hubei and Hunan are at risk of heatstroke and should take precautions to keep cool - including the avoidance of extended outdoor activity.

Hot weather will continue in China's eastern and northwestern regions until the end of this month, according to the center's forecast.

The center found that heat-affected areas have expanded since July 10, and that across more than 1.38 million square kilometers - about one-eighth of the Chinese mainland - high temperatures exceeded 35 C through Sunday, and across one area of 65,000 square kilometers it exceeded 40 C.

But the ongoing heat has not beaten the records set in 2013, when China's vast eastern regions saw a run of more than 40 sweltering days in July and August.

"But it has seen an increasing number of days with high temperatures due to global warming," said Xiao Chan from the center.

He added that the number of days with high temperatures in the Yangtze River's middle and downstream areas have increased by 0.7 days every 10 years.

Shanghai, one of China's most populated cities, has experienced lingering heat for the past 15 days, topping major capital cities in the amount of days with temperatures higher than 35 C. It also set a record high of 40.9 C on Sunday, the highest in 145 years.

"It's like walking in an oven," Shanghai resident Zhang Jiawei said on Tuesday. "It makes me sad that the heat will continue for days more. I can't breathe or sleep without the air conditioner, which has worked day and night."

In addition, many cities in regions neighboring Shanghai also saw records. For example, Jiashan, Zhejiang province, hit 41.1 C, while Changzhou, Wuxi and Changshu in Jiangsu province hit 40.9 C.

The lingering subtropical high pressure area and hot winds are to blame, the center's Xiao said.

Many families shared Zhang's experience with their air conditioners - leaving them on constantly. That has caused electricity consumption to soar to record highs in many provinces, including Zhejiang, Shaanxi and Hubei.

In Hubei, electrical consumption hit a record high on Monday, of which 40 percent went to support air conditioners. Consumption is expected to increase even more in the next few days, according to the Hubei branch of State Grid Corp of China.

At the same time, the lingering heat in central and eastern regions is good for rice harvesting and drying, but could cause drought in some places. Also, the heat could harm some vegetables and fisheries, authority said on Tuesday.