A series of sinkholes appearing across the country has highlighted growing concerns over safety as underground construction projects are carried out in various locations.

The most recent incident occurred Monday morning near a metro extension construction site in Busan’s Sasang District, which has seen 14 sinkholes over the past three years. A sinkhole, approximately 3 meters wide and 2 meters deep, appeared 200 meters away from another one that measured 5 meters wide and 3 meters deep, which appeared just a day earlier.

Followed by a collapse at a subway construction site in Gwangmyeong, Gyeonggi Province, on Friday, Seoul also saw multiple sinkholes over the weekend.

According to safety and emergency offices, a sinkhole opened at a crossroad in Gangdong District on Sunday, just three kilometers away from where a 20-meter-wide, 20-meter-deep sinkhole opened at an intersection last month, killing a motorcyclist. This is the third sinkhole in the district recently after another sinkhole appeared near an elementary school earlier this month.

Meanwhile, in Seoul’s Mapo District, another sinkhole, 40 centimeters wide and 1.3 meters deep, appeared on Sunday morning.

Although casualties or property damage were reported in these sinkhole events, concerns are growing over whether the country’s safety regulations on urban underground development are being followed.

Korea has seen a growing number of sinkholes, mostly in highly urbanized areas.

According to data from the Seoul Metropolitan Government, Seoul has seen 63 sinkholes in the past three years since March 2022. Among them, 30 percent happened in southern Gangnam areas.

The Ministry of Land, Infrastructure and Transport’s Underground Safety Information System shows that 451 sinkhole-related accidents took place across the country between March 2022 and March 2025.

A giant sinkhole that appeared on March 24 and killed a motorcyclist is seen in Seoul's Gangdong District, in this March 28 photo. Yonhap

While the cause of the incidents is still under investigation, sinkholes are commonly observed during spring, when frozen ground thaws, and during the summer monsoon season. Government data shows that nearly 76 percent of all sinkhole incidents across the country have occurred during these two seasons since 2018, with 371 cases in spring and 647 in summer, out of a total of 1,345 incidents.

Data shows that the main causes of sinkholes are excessive underground development, the rupturing of old water supply and sewage pipes, groundwater leakage and ground instability caused by underground construction projects.

Notably, damage to sewage pipes ranked as the top cause of sinkhole incidents in Seoul between March 2022 and March 2025, accounting for 26 out of 63 cases. Other contributing factors included poor soil filling, inadequate ground excavation work and water pipe damage.

"If the ground near the construction site is soft and sandy, there is a greater risk of sinkholes," said Hong Sung-gul, a professor at Seoul National University. "The scope of underground water impact investigations should be significantly expanded before starting any underground development in the city."

In response to a series of sinkhole incidents, the Seoul government plans to conduct ground penetrating radar exploration to check the risk of ground subsidence in major construction sites in the capital.