BEIJING -- During a recent weekday lunch, middle-aged Wu Zhixin had a plate of shredded pork noodles glistening with oil and washed it down with a paper cup of vodka-like alcohol. Then she lit a cigarette.

"No smoking," a waitress called out. Wu nodded, but finished her Double Happiness brand cigarette before stubbing it out on the tiled floor.

Scenes like this are typical and illustrate the challenges China faces in tackling the explosion of chronic diseases such as heart disease and cancer, two top killers here.

"I smoke because I work in sales and it helps me cope with the stress of meeting targets," said Wu, a slightly overweight woman who smiles warmly but has stained teeth. "I know it is bad for me and I'm trying to quit, but I'm still very healthy now, and I'm optimistic about my future."

Newly prosperous, China is facing a very changed health picture from a generation ago when it was still largely poor and agrarian -- and the diseases plaguing Chinese have changed too.

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Heart disease, cancer, and respiratory disease have replaced hepatitis, diarrhea and malaria as desk work replaces farming, cars replace bicycles, and smoking remains stubbornly popular.

Chronic diseases account for more than 80 percent of deaths in China, or nearly 8 million in 2008, according to the World Health Organization. The epidemic comes as the UN General Assembly holds a high-level meeting on noncommunicable diseases next week.

Compared with the United States, China has three times the death rate from respiratory diseases like emphysema. By another measure, Chinese are healthier, with only a quarter of the population overweight, compared with two-thirds of Americans.

China's breakneck economic development over the past 30 years has pulled hundreds of millions out of poverty and moved many people into cities.

But a broken health care system and inadequate state insurance mean getting treated for serious diseases can impoverish many families. Unhealthy diets and sedentary lifestyles have helped accelerate an explosion in chronic diseases.