Namdaemun Burns - a nation mourns

A 600-year-old gate in central Seoul listed as South Korea's number one national treasure has been destroyed by a likely arsonist, police have said.

Namdaemun, or "Great South Gate", was engulfed in flames late on Sunday, they said.

Police said they were searching for a man who is suspected of breaking into the stone and wooden structure and starting the fire.

"From what we can see, except for the pillars on the first floor, the gate has been completely burnt down," said a fire official.

The wooden pavilion on top of the gate's stone base was reduced to a smouldering hulk by the fire.

The gate was constructed in 1398 and served as the main southern entrance for Seoul when it became Korea's capital more than 600 years ago and was a walled city, the Cultural Heritage Administration said.

The structure, also called Sungnyemun or "Gate of Exalted Ceremonies", has been rebuilt several times, with the most recent renovation taking place from 1961-1963.