DALIAN, Liaoning - Heavy fog shrouded this coastal city in Northeast Chinas' Liaoning province, threatening the lives of those who still rely on burning coal for heating in the winter.

Two big hospitals in the Lushunkou district - the No 406 Hospital of the People's Liberation Army and the People's Hospital of Lushunkou District - started at 10 pm on Saturday to admit patients who had suffered from carbon monoxide poisoning.

Within 24 hours, they had accommodated 39 sufferers from nine communities, the district government said on Monday. They all live in bungalows heated by coal stoves.

A 10-year-old girl named Meng Li died on her way to the hospital while her mother remained in a deep coma. The other 37 people were in a stable condition and had been discharged from hospital, according to the district government.

Meng Li and her mother lived in a bungalow. Their landlady, surnamed Zhou, found them poisoned at around 9 pm on Saturday.

"When their door remained closed at 9 am, I sensed something was wrong, since the two always got up very early," Zhou told China Daily on Monday.

"So I called some other neighbors and managed to break into the room, to find the mother and her daughter lying in bed unconscious."

Zhou said the coal-fuelled stove proved to be lethal. "We had warned Meng Li's mother about the danger, but the tragedy still happened."

Unlike most urban families in Dalian who have central heating, some people living in bungalows still rely on coal-fuelled stoves for heating, putting them at risk for carbon monoxide poisoning.

The heavy fog, which started to shroud Dalian on Saturday, increases such risks. Firmly-shut windows, low air pressure and stagnant air on foggy days make carbon monoxide hard to dissipate, says Li Xuewen, head of the oxygen therapy center under the No 406 Hospital of the People's Liberation Army.

"In this situation, the soot discharged outside easily flows back into the room. As a result, poisoning occurs in closed rooms," he was quoted as saying.