Updated from 11:02 a.m. EDT

Shares of the No. 1 Chinese job-search company, 51Job ( JOBS - Get Report), dove 20% Monday after the company told analysts it saw signs of a slowdown in China's explosive growth.

51Job's stock was recently down $4.23, or 20.7%, to $16.21, despite reporting a jump in first-quarter profits. Its net income reached 9.2 million Renmibi, or $1.1 million, for the quarter, up from 8.8 million Renmibi in the same quarter last year. Its total revenue rose 30% to 142.7 Renmibi, or $17.2 million.

The bad news came in its conference call with Wall Street that followed its earnings announcement. Executives told analysts that the company was seeing a moderation in market demand this year that could be evidence of lower business investment and a slowing economy.

"They see some softness in job listings that could represent some slowing in economic activity that is not showing up in the Chinese government's GDP growth data," said Chang Hua Qui, analyst with Forun Technologies (he does not own shares in 51Job, and his firm has not investment banking relationship with the company). "But remember that the Chinese government is trying to slow the economy's growth in order to maintain sustainable growth and avoid booms and busts. So, in that sense, this news could be viewed as a positive for the Chinese economy, since its recent growth rates are not sustainable."

The Chinese economy has rapidly become one of the fastest growers among world markets in recent years as it has joined the World Trade Organization and opened its economy to more competition. Last year, the U.S. stock market stalled several times over concerns that China was in danger of overheating.

51Jobs is only one company in that huge nation. Still, given some of the fuzziness of official economic data there, the online recruiter's observations could be viewed as an independent barometer for China.

Aside from being a major trade partner with the U.S. and an extensive buyer of U.S. debt securities, China also represents one of the most anticipated growth markets for major U.S. companies, including Wal-Mart ( WMT) and Starbucks ( SBUX).

Despite its cautionary comments about the Chinese economy, 51Jobs sounded a positive note about its first-quarter performance.

"In the online recruitment services business, we saw a greater number of first-time customers as well as an increase in the number of clients choosing our more sophisticated visibility packages to attract job seekers during the peak period," the company said. "We also experienced an increase in candidate placements in our executive search business and gained momentum in our other human resource related services with additional HR outsourcing contracts."