Natural gas-fired water heaters and cooking stoves have become more common in China as living standards have risen, replacing older coal and wood-powered devices. Water heaters in bathrooms, where carbon monoxide can accumulate quickly in a small space, appear to be deadliest of all, the reports said.

“It’s often the case that by the time medical workers break into the door, it’s already too late,” Yang Shixiong, the director of an emergency medical center in Nanning, the capital of Guangxi, told China National Radio. “Every winter there are many reports like this, but every year it’s the same, and there’s no clear improvement.”

The reports did not say how the death rate this winter compared with previous ones.

But some medical experts in Guangxi suggested that the carbon monoxide deaths reflected growing use of poorly installed gas heaters, as well as an unusually long and sharp cold spell across the region. Too many residents turned on faulty heaters and then shut windows and doors to keep in the warmth, trapping in the gas, they said.

Each year, more than 400 Americans die from unintended carbon monoxide poisoning, according to the Centers for Disease Control and Prevention. China does not release similar nationwide estimates, but the number is likely to be much higher.

The reports of poisonings in Guangxi gave examples of whole families overcome by carbon monoxide. In the city of Liuzhou, ambulance workers found a family of three on Wednesday that had apparently been killed by the gas — the mother in the bathroom, the father in a bedroom doorway and their daughter on a bed, the official Guangxi news service reported. In another city, a father and his 2-year-old son died in the shower.