South Korean tech giants said Wednesday no damage has been reported at production plants following the magnitude 5.4 quake which struck the southeastern city of Pohang earlier in the day.
No casualties have been reported and it is still unclear whether a tsunami warning will be issued.
North Korea and South Korea are located in the region known as the Ring of Fire - which extends around the Pacific Ocean and is a hotspot for quake activity.
Nuclear reactors in the region operated normally when the nation's strongest-ever quake at magnitude 5.8 hit Gyeongju in September 2016.
The weather service revised the magnitude from an initial 5.5 to 5.4 after a rigorous analysis.
Tremors were felt around the country, including in Seoul and Busan. USGS reported the tremor struck at a depth of 10km at 2.29pm (1.29pm, Singapore time). An aftershock of 3.6-magnitude took place in an area 7 km north of the coastal city, followed by third and fourth shocks.
South Korean media showed crumbled walls piled on parked cars, broken windows from some buildings and elementary school students taking shelter on a playground. Electric lamp hanging from the ceiling was shaken, with books falling from a bookshelf.
Photos and video footage sent to local TV stations showed crumbled street walls and furniture violently shaking inside people's homes and people rushing out of buildings in panic.
Pohang is some 35km from the Wolseong Nuclear Power Plant, which has six operational reactors. Moon convened an emergency meeting with his secretaries.
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