At least eight people were injured, with lots of property damage reported, as South Korea was hit by the country's biggest ever earthquake on Monday night, Seoul's safety ministry said.
As of 5 a.m. local time on Tuesday, eight people had been confirmed wounded, but they sustained minor injuries, according to the Ministry of Public Safety and Security (MPSS).
More than 250 cases of property damage were reported, including building cracks, water pipe rupture and roof damage.
Buildings suffered from heavy shaking, leading people to run out, according to TV footage. Roofs of some of homes came down, and bricks fell from housings. Cracks were found in roads and apartment buildings, showing the severity of the quakes.
A 5.8-magnitude earthquake, the strongest ever hitting the country, struck on the outskirts of Gyeongju city in North Gyeongsang province at about 8:32 p.m. local time (1132 GMT) on Monday.
The main shock occurred less than an hour after a 5.1-magnitude quake, the fifth-biggest faced by South Korea, rattled the nearby region at 7:44 p.m..
As of 2 p.m. on Tuesday, some 250 aftershocks followed, according to the Korea Meteorological Administration (KMA) which forecast secondary shocks of two to four magnitudes would last for three to four days.
The big tremors were felt nationwide from adjacent cities of the epicenters to as far north as capital Seoul and far south as the southern resort island of Jeju.
The epicenters of the two quakes are located just 1.4 km away from each other southwest of Gyeongju, near which multiple nuclear power plants and a radioactive waste disposal facility are sited. The majority of the country's nuclear power stations are located along the east coast.
Korea Hydro and Nuclear Power (KHNP), the country's nuclear power plant operator, said its atomic power plants suffered no damage, but it turned off four nuclear reactors at the Wolsong nuclear power plant at around midnight on Monday for a safety inspection.
In the adjacent eastern coast city of Ulsan, a thermal power plant suspended operations following the series of quakes.
Concerns emerge here that South Korea is no longer a safety zone from seismic activity as earthquakes of 5.0 magnitudes or higher have happened three times in 2016 alone.
A 5.0-magnitude quake struck in waters some 52 km east of Ulsan city on July 5. The North Gyeongsang province has been hit by quakes 62 times in the past 10 years, including Monday's two tremors.
South Korean President Park Geun-hye ordered government officials to comprehensively review the country's earthquake response system following the series of powerful earthquakes.
Park chaired a cabinet meeting in the presidential office on Tuesday, instructing officials to thoroughly brace for possible quakes of higher seismic intensity than Monday's tremors.
She ordered a full review of countermeasures to protect major facilities, including nuclear power plants and radioactive waste disposal facilities, from violent quakes.
The president said the latest quakes became a wake-up call to the perception that South Korea is relatively a safe zone from earthquakes.
