No visitors or cultural heritage items were damaged.
The fire started around 8:40 AM on the third floor, spreading to the fourth.
Firefighters issued a Level 1 response within 50 minutes, deploying 76 equipment units and 262 personnel.
The flames were largely controlled by 12:31 PM, but it took additional time to clear residual embers.
The fire was fully put out by 3:22 PM.
One firefighter was injured, and six workers evacuated safely.
The museum had been closed for expansion work since last October, preventing additional casualties.
The third and fourth floors were destroyed, but no cultural heritage losses were reported.
Key artifacts had been relocated earlier to the National Museum of Korea.
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