Two earthquakes with the magnitudes of 5.5 and 5.4 have struck off South Korea's southeastern coast, about 6km north of the port of Pohang, the national meteorological service said.
It's the strongest quake in South Korea since a 5.8-magnitude occurred near the ancient city of Gyeongju, which is close to Pohang, in September 2016, Korea Meteorological Administration officials said.
The outer wall of an elementary school in Pohang has fallen after a magnitude 5.5 quake hit the southeastern city on November 15, 2017.
The Cultural Heritage Administration said Wednesday that there is no immediate damage detected to historic buildings and artifacts in Gyeongju, a city adjacent to earthquake-struck Pohang.
Joo Koon train incident was second collision in MRT history
Transit operator SMRT said 23 passengers and two staff suffered light to moderate injuries and have been taken to hospital. A commuter, Mei Anne posted on her Facebook page saying that she was on the train which collided with the other train.
South Korea has relatively little seismic activity, compared with Japan to the east.
Images posted on social media showed shattered storefronts, goods tumbled off store shelves, cars smashed by fallen bricks and cracks on the ground.
Korea Hydro & Nuclear Power (KHNP) said the six nuclear reactors in Gyeongju, about 45 kilometers south of the epicenter, as well as other reactors on the southeastern coast are all functioning normally. The Pohang natural disaster is the strongest Korea has experienced since 2016, after the magnitude 5.8 quake in Gyeongju.