A 600-year-old gate has collapsed just five hours after being overtaken by fire late Sunday.

Authorities said some 100 firefighters and 60 firefighting trucks were sent to control the fire at Sungnyemun, more commonly known as Namdaemun. The blaze began around 8:50 p.m.

But their efforts were stymied because of the wooden gate's waterproof construction.

Police suspect arson as witnesses say the fire started after a man with a shopping bag was spotted going in and out of the gate.

However, they are also investigating the possibility of a short circuit.

In addition, police said they'll look into whether agencies that manage the gate, including the Cultural Heritage Administration, followed proper management procedure.

Namdaemun had been designated the nation's Number-One national treasure and was the oldest wooden structure in Seoul. Construction of the gate began in 1395 and was completed in 1398 during the rein of King Taejo, who founded the Joseon Dynasty.