BEIJING, July 7 (Xinhua) -- China's insurance sector saw premium income drop 5.9 percent year-on-year to 1.9 trillion yuan (about 286 billion U.S. dollars) in the first five months, according to official data.

The decline came as authorities enhanced regulation of the sector to defuse financial risk.

Property insurance firms posted a 15.3-percent increase, but life insurance companies, which account for over 70 percent of the total premium income, registered a 11.5-percent dip, data from the China Banking and Insurance Regulatory Commission showed.

Outstanding investment by insurers reached 15.5 trillion yuan as of the end of May, up 4.2 percent from the start of the year.

Total industry assets stood at 17.5 trillion yuan at the end of May, representing an increase of 4.5 percent from the beginning of the year.