South Korea has the highest employment rate of seniors among advanced countries due to the rapid aging and insufficient social welfare system, data said Monday.

The employment rate of South Koreans aged 75 or older reached 17.9 percent in 2015, ranking first among 25 members of the Organization for Economic Cooperation and Development, according to the data compiled by the Paris-based agency. It is far higher than the OECD average of 4.8 percent.

Mexico came next with 17 percent, followed by Japan at 8.3 percent, Portugal at 6.6 percent and New Zealand at 6.1 percent.

Moreover, for seniors who are 65 years or older, South Korea's employment rate came in second with 30.6 percent in 2015 after Iceland that posted 38.7 percent. The OECD average was 13.8 percent in the same year.

Analysts noted that the country's lax social welfare and pension system is forcing old people to remain at work even after retirement in order to earn a living.

Separate data showed that Asia's fourth-largest economy had the highest senior poverty rate of 63.3 percent in the OECD in 2015.

"South Korean old people have not prepared for retirement so they have to land paying jobs," said a report published by the Seoul Institute. (Yonhap)