As the temperature soars during the summer, heatstroke becomes a genuine health concern that warrants serious attention, experts have warned.

"Heatstroke is a medical emergency, and can be fatal if not treated promptly and with care," said Gu Chengdong, vice-director at the Emergency Department of the China-Japan Friendship Hospital.

When temperatures are very high or when a person does strenuous physical activity in a hot environment, the body will be unable to balance heat gain and heat loss through evaporation of sweat. The body temperature rises causing illnesses such as heat syncope, heat tetany, heat exhaustion and heatstroke.

A person will usually suffer from heatstroke when the body temperature exceeds 40 C.

Heatstroke can kill cells, disrupt the central nervous system and metabolism, and result in organ failures that could prove fatal, Gu said.

"Children, the elderly, outdoor workers, new mothers and people with chronic diseases are all at higher risk of heatstroke," said Liao Shaofang, director at the Emergency Room of Tsinghua University No 1 Hospital.

"The human body cannot reduce temperature efficiently in a hot and humid environment. Some people refuse to use air-conditioners and fans because they fear the cold or want to save money, and some people try to do too much in a hot environment. It's very unwise to do such things."

Liao said he still remembers a 17-year-old girl he failed to rescue in 2009. The girl worked in a restaurant, her job was to make steamed buns.

She fainted suddenly at work, when she was sent to Liao, her body temperature had soared to 42 C.

Although the medical team used ice sheets and life-support measures, she passed away when her kidneys and heart failed.

"There is almost no chance of recovery if the heatstroke is as severe as causing multiple-organ failure," Liao said.

In recent years, as the authorities have realized the potentially fatal danger of heatstroke to outdoor workers, and issued new guidelines on how to deal with very high temperatures. Cases of heatstroke in outdoor workers have become rare in the emergency room, but ordinary people still seem unaware of the dangers, said Gu.

Liao said the majority of heatstroke patients in his hospital are elderly people with low immunity, especially those with chronic diseases, new mothers who remain inside enclosed rooms to avoid wind, following a Chinese tradition, and children who have weak physical fitness.

But heatstroke is easy to prevent. Gu said he recommends avoiding spending long periods in a hot and humid environment, eating a light diet in summer and drinking light salt water after sweating.

"Prevention is better than cure," Gu said. "It is a pity that people overlook the problem as it can cause trouble for them."