BEIJING, Dec. 1 -- Wang Hong, a 31-year-old woman and stay-at-home mother in South China's Haikou City, is worried about her future pension as she stopped paying social insurance four years ago.

After paying the insurance for five years while at work, Wang quit her hotel job to look after her child. With her child now 3 years old, Wang Hong, not her real name, is looking for a new job. But she is hesitant about paying the insurance she has missed for the past four years.

"I don't know what will happen to my money in a social insurance account with possible inflation and other risks. It feels safer to keep it in my own pocket," she said.

In China, 38 million people stopped paying social insurance this year, either before or after reaching the pension-receiving threshold of 15 years.

Laid-off workers, employees in cash-strapped small companies and migrant workers are the majority of those who have stopped paying the insurance halfway through, according to Cui Peng, a research fellow with People's Insurance Company of China.

Social insurance funds cover basic endowment for senior citizens, basic medicare, unemployment, work-related injury and maternity.

The spending of endowment insurance funds, a key part of social insurance, grew 22 percent in 2012 year on year, while its revenue increased by 19 percent, according to the Ministry of Finance last week. This poses challenges for future pension payments.

According to the Ministry of Human Resources and Social Security, at the end of 2012 about 210 million urban employees paid endowment insurance.

Endowment insurance is paid by staff and the company, 8 percent and 20 percent of his or her wage respectively.