About 600,000 migrant workers left south China's industrial heartland last year as the economic crisis caused exports to shrink and forced factories to close, a senior official said Thursday.

The number of migrants departing Guangdong province, one of the world's top makers of toys and electronic appliances, accelerated through 2008 as the global situation worsened, said provincial deputy governor Huang Longyun.

"This year the situation is more serious than at any other time since the start of the decade, indeed since the Asian financial crisis," he told a briefing in Beijing, referring to regional turmoil that broke out in 1997.

By the middle of last year, when the economic crisis was still in its embryonic stage, only 143,100 workers had left Guangdong, but the number reached half a million at the end of October and has now hit 600,000, he said.

Guangdong's export sector has been one of most important factors in China's phenomenal economic boom, and it has been helped by migrant workers who have gone to the province from China's destitute interior in search of better lives.

Huang did not give an overall figure for migrant workers in the province, but earlier data said they numbered between 25 and 30 million.

The situation is likely to become even worse in the next few months, according to Zheng Zizhen, an expert on population issues at the Guangdong Academy of Social Sciences, a government think tank.

"If the economic conditions continue to deteriorate, I would not be surprised if there are one million to two million more migrant workers leaving the province this year," he told AFP.

Data unveiled at the briefing showed the region's economic growth slowed to 10.1 percent last year, down from 14.7 percent in 2007.

Exports, the lifeblood of the province, expanded by just 5.6 percent in 2008, down from 22.3 percent the year before.

The health of Guangdong is essential for China's overall wellbeing, as the Pearl River Delta, the province's most active economic area, provides much of the nation's growth impetus.

Together with the Yangtze River Delta further north it takes up just 2.6 percent of China's land area, but accounts for one third of its gross domestic product and 40 percent of its fiscal revenues, according to government data.

The release of the data comes as China's communist leaders grow increasingly concerned about the impacts the economic crisis may have on social stability in the nation of 1.3 billion people.

The official jitters were expressed in unusually candid terms this week in the authoritative weekly magazine Outlook, published by the state-run Xinhua news agency.

The magazine warned of the rising risk of social disturbances, or "mass incidents", pointing out that nationwide 10 million out of 120 million migrant workers had lost their jobs.

The magazine quoted Huang Huo, a senior Xinhua reporter, as saying that one of the most sensitive periods of 2009 would be after the Lunar New Year period in late January and early February.

Once the holiday is over, millions of migrant workers will return from their rural homes to the big cities along the coast, and many may end up frustrated in their search for work.

"There's absolutely no doubt that we've entered into a period of rising mass incidents, and in 2009 China could face more conflict," Huang told the magazine.

China's export-dependent economy as a whole could grow by just 7.5 percent this year, the World Bank said recently, which would be the lowest level in 19 years.