The incident occurred on June 9 as the bus was travelling from Yen Nghia Bus Station to Kim Ma Bus Station. The falling debris shattered a side window and damaged part of the vehicle's exterior.
The driver stopped immediately after the incident and reported it to operators. Authorities later arrived at the scene to investigate.
Ta Vinh Khang, director of Hanoi BRT Bus Enterprise, said neither the driver nor passengers were injured. The damaged bus was subsequently sent for repairs.
Hanoi Metro, which operates the Cat Linh-Ha Dong line, confirmed the incident and said the fallen material came from a decorative plaster layer surrounding a station sign, rather than any load-bearing structure.
The operator said the decorative layer, about 5 cm thick, had no reinforcing mesh. Prolonged exposure to weather conditions and vibrations during operation had caused cracks to develop, eventually leading to the detachment.
Hanoi Metro said the incident did not affect the structural integrity of the station or metro operations.
The company added that it would inspect similar decorative structures across the line to prevent similar incidents.
The Cat Linh-Ha Dong line, Hanoi's first metro route, entered commercial service in November 2021. The 13-km elevated railway includes 12 stations between Cat Linh and Yen Nghia and serves tens of thousands of passengers each day.
