A tower at the historic, quake-damaged Kumamoto Castle in southern Japan -- one of the country's three premier castles and once a major tourist attraction -- has collapsed, an official said Thursday.

Heavy rain at the castle -- originally built in 1607 during Japan's feudal era -- caused a stone wall supporting the structure to crumble. The spectacular collapse came amid a 20-year project to repair damage to the castle following a series of devastating quakes in April 2016.

The castle complex is surrounded by hundreds of cherry trees and was once a huge tourist draw, but had been closed to the public since the quakes. The damaged "Mototaiko Yagura" tower was located close to the main gate of the castle, Tatsuo Nomoto, a municipal official at the castle, told AFP.