* Slowdown spreading to services sector
* Slowest growth since August 2011
* Employment falls for first time since Jan 2009 (Adds comment)
BEIJING, May 6 (Reuters) - Growth in China's services sector slowed sharply in April to its lowest point since August 2011, a private sector survey showed on Monday - fresh evidence of rising risks to a revival in the world's No.2 economy.
The HSBC services Purchasing Managers' Index (PMI) fell to 51.1 in April from 54.3 in March, with new order expansion the slowest in 20 months and staffing levels in the service sector decreasing for the first time since January 2009.
Two separate PMIs last week had already shown that China's manufacturing sector growth slowed, With the weakness spreading to services, which make up almost half of gross domestic product, the risk to the recovery may be increasing.
"The weak HSBC service PMI figure provides further evidence of a slowdown not only in the factory sector but also in the service sector," said Zhang Zhiwei, chief China economist at Nomura Securities in Hong Kong.
"This confirms our worries about insufficient growth momentum in the economy, which we expect to slow to 7.5 percent in the second quarter."
The HSBC services PMI follows a similar survey by China's National Bureau of Statistics, which found non-manufacturing activity eased to 54.5 from 55.6. The official PMI is more weighted towards large state-owned firms.
Readings above 50 indicate activity in the sector is growing, while those below 50 indicate it is contracting.
The HSBC survey showed that the sub-index measuring new business orders dropped sharply to a 20-month low of 51.5 in April, with only 15 percent of survey respondents reporting an increased volume of new orders that month, HSBC said.
"This started to bite employment growth. All these are likely to add some risk to China's growth in 2Q, as there's still a bumpy road towards sustaining growth recovery," said HSBC's China chief economist Qu Hongbin.
The employment sub-index decreased to 49.6 in April, the first net reduction in staff numbers since January 2009, although HSBC said job losses were marginal, partially caused by firms down-sizing and employee resignations.
Employment is a decisive factor shaping government thinking because it is crucial for social stability. The services sector accounted for 46 percent of China's gross domestic product in 2012, as big as the country's better-known manufacturing industry.
China's economic growth unexpectedly stumbled in the first quarter, slipping to 7.7 percent versus 7.9 percent in the previous three month period, as factory output and investment slowed.
The government has set a 2013 growth target of 7.5 percent, a level Beijing deems sufficient for job creation while providing some room to reform to the economy.
Any more weak data could spark a policy response.
"The risk of slower growth is rising, the Chinese government will probably take actions after April data come out," said Jianguang Shen, chief China economist of Mizuho Securities Asia in Hong Kong.
"I see an increasing possibility for China to cut interest rates, but not likely any time in the near future, as housing inflation is a constraint."
However a Reuters poll last month found that China's central bank is expected to keep the benchmark one-year bank lending rate at 6 percent and the one-year bank deposit rate at 3 percent through 2013, as well as holding banks' reserve requirement ratios (RRR) steady. (Reporting By Beijing economics team; Editing by Eric Meijer)