The population of Seoul has fallen below 10 million for the first time in 28 years with registered citizens at 9.99 million last month, Statistics Korea said Tuesday.

The population of the capital surpassed 10 million in 1988 and stayed above until now. As of March, 10 million people were registered as living or having a residence in Seoul, but the number falls below that mark if 10,472 who live abroad are excluded.

The main reason for the decline is an exodus to the suburbs in surrounding Gyeonggi Province. Seoul first saw a net outflow of 2,300 citizens in February 2009, which has continued ever since. Last year it increased to 8,820, the biggest of all metropolitan cities in the nation. Gyeonggi Province by contrast saw a net influx of 9,264 citizens last month, the biggest in the country.

Lee Ji-yeon at Statistics Korea blamed soaring home prices.

