South Korea's birth rate hit a four-year low last year as more couples delayed marriage in the economic downturn, officials said Thursday.

Statistics Korea said the birth rate - the average number of babies born during a woman's lifetime - was 1.15 in 2009, the lowest since 1.08 in 2005.

Some 445,000 babies were born last year, 4.4 percent down from 466,000 in 2008.

"South Korea would have the world's lowest birth rate were it not for some city-states such as Singapore and Hong Kong," Kim Dong-Hoy, who handles the population issue at the statistical body, told AFP.

"It is largely due to a growing number of couples who delay or shun marriage amid an economic downturn."

The number of marriages decreased five percent year-on-year in 2009 while the divorce rate increased eight percent.

South Korea has offered a variety of incentives to encourage people to have children. Officials fear a shrinking workforce will hit growth and will be unable to foot the bill for a rapidly ageing population.

The health ministry last month said it was turning off the lights in its offices once a month to encourage staff to go home early and make more babies.

Authorities warn that the population, currently almost 50 million, could start declining within a decade.