The summer heat wave is forecast to continue this week and expand over more of the country, and people are being warned to protect themselves.

On Monday, the National Meteorological Center issued a new yellow alert - the lowest level in a three-tier warning system for heat. The alert, initially issued on Friday, means temperatures over 35 C can be expected for three more days.

North China, Northwest China, the Inner Mongolia autonomous region and areas immediately south of the Yangtze River have seen temperatures above 35 C.

Record highs were set on Sunday in 11 counties in the Xinjiang Uygur autonomous region and Gansu and other provinces, with the highest being 47.8 C in Turpan, a city in Xinjiang.

The area hit by the heat wave in northern China will continue to expand in the coming 10 days, and southern China will see very hot weather that lasts for four to nine days, said Sun Jun, chief weather forecaster at the meteorological center.

Some areas, like Beijing, may get some relief this weekend, with temperatures forecast to drop below 35 C.

The heat wave in the south is a result of subtropical ridge, a belt of atmospheric high pressure characterized by mostly calm and warm winds from tropical regions, while the hot weather in the north is mainly due to another warm high pressure formed on the continent, said Sun said.

While the heat wave is making conditions uncomfortable, it is not particularly severe compared with other years, like 2013, Sun said.

Still, the heat can increase the risk of life-threatening heatstroke, said Gu Chengdong, deputy director of the emergency department at China-Japan Friendship Hospital in Beijing. Heatstroke can happen when the body temperature hits 40 C, at which point cells can be damaged and the nervous system can be harmed. Fatal organ failure can follow, Gu said.

Gu suggests reducing time outdoors, especially during the hottest time of the day, usually from 10 am to 3 pm.

Li Lei contributed to this story.

A huge thermometer shows surface temperatures hit 88 C in Turpan, Xinjiang Uygur autonomous region, on Sunday.Liu Jian / For China Daily