beijing (Bloomberg) — Dai Chen broods as train No. 1076 rumbles across south China's Guangdong province, taking him back to the fields and trees of his rural home. He'd rather be on the noisy, cramped factory floor in Dongguan where he used to work.

"There's nothing to do in the countryside except be a farmer," Dai, 21, says while smoking a Baisha cigarette in the dark corridor between cars. "I don"t want to be a farmer."

As many as 20 million migrants may leave coastal cities next year as the worst financial crisis since the Great Depression shutters factories making everything from clothes to toys and computers, economists estimate. Until now migration has been a safety valve for China, with the population of rural areas dropping by 140 million since 1999.

As workers return to the countryside, where wages are a third of those in the cities, there is growing concern among China"s leaders that rising tensions could undermine the Communist Party, which came to power 60 years ago in a peasant revolution. Fired workers smashed motorcycles and damaged company equipment during demonstrations last month in southern Guangdong.

"The government is quite nervous about the situation among migrant workers and the rural population," says Willy Wo-Lap Lam, adjunct professor of history at the Chinese University of Hong Kong. "The legitimacy of the regime is based solely on its ability to improve people's living standards. If it can't deliver improvement, its legitimacy could be fractured."

The No. 1076 to Chongqing, 24 hours and 1,050 miles away, represents dashed dreams for the migrants who file on lugging their belongings in burlap bags.

Men sweating from the strain of stuffing their bags into overhead racks sit bare-chested in blue upholstered seats. Women chat in a mix of village dialects and Mandarin while spitting sunflower seed shells onto the floor and slurping instant noodles from paper cartons.

The train snakes from Guangdong's capital through rural Hunan and Sichuan provinces, which supplied the cheap labour that powered China's economy for three decades. Now demand for labour is slowing with China"s economy.

Gross domestic product will grow 7.5 percent next year, the slowest in almost two decades, the World Bank forecasts. China has averaged 9.9 percent annual growth for the past 30 years.