China Life Insurance Co. said Wednesday that it expects to see a 40 to 50 percent year-on-year drop in its net profits for 2011when the data is audited.

China Life, the country's biggest life insurer, posted a net profit of 33.63 billion yuan (5.33 billion U.S. dollars) in 2010.

The auditing process should be completed by late March or early April.

In a statement filed to the Shanghai Stock Exchange, the Beijing-based insurer attributed the slump to declining investment yields and rising impairments caused by market fluctuations.

China's stock market posted sluggish performance in 2011, as the benchmark Shanghai Composite Index fell 21.68 percent year-on-year.

Meanwhile, slower growth in the country's life insurance premium incomes could also be to blame for the company's declines.

China's life insurance premiums dropped from 1.05 trillion yuan in 2010 to 956 billion yuan last year, according to data from the China Insurance Regulatory Commission.

Shares in China Life slid 1.07 percent to close at 17.5 yuan on Wednesday.