The population of Seoul fell under 10 million for the first time in nearly three decades, government data showed Wednesday, apparently due to soaring housing prices in the country's capital.

Seoul's population came to 9,995,784 as of the end of May, down 7,195 from a month earlier, according to the data released by the Ministry of the Interior. It has not dropped below the 10-million mark since the capital became a mega city in 1988.

The number has been decreasing for 15 consecutive months since March last year, according to data. During the cited period, the population shrank by 109,422.

"The drop below the symbolic 10-million mark in population is a new change," said Eun Ki-soo, a professor at Seoul National University. "Considering the decrease in overall population due to the nationwide low birthrate and exorbitant housing costs, it is unlikely that Seoul will be able to regain the 10-million mark down the road."

According to moving-in reports made by those who left Seoul, housing was the most frequently cited reason, said Lee Ji-yeon, an official at Statistics Korea.

"Previously, birthrate often contributed to the increase in Seoul's population, but now with the low birthrate trend, it (population) is mostly decided by people moving," she added.

The government's recent data showed that the fertility rate, or the average number of babies that a woman is projected to have during her lifetime, stood at 1.24 in 2014, well below the proper level of 1.8 needed to sustain the current population.

Meanwhile, the population in Gyeonggi Province, surrounding the capital, increased by 6.85 percent to some 12.5 million from 11.7 million in 2010, the data showed, indicating the expansion of the capital area.

"Though the number of residents decreased due to housing issues, the daytime population who wish to study, work and benefit from diverse services in Seoul is still high," professor Eun said.

South Korea's overall population increased by 0.36 percent to some 51.6 million from a year earlier. (Yonhap)