At around 5:20 p.m. passengers were surprised to see water dripping continuously from the ceiling.
Some opened umbrellas while others moved to different spots.
On Tuesday morning, the Hanoi Metro Co., Ltd., the operator, issued a statement saying the cause of the leak was a fault in the air conditioning control system.
A drainage problem in the air-conditioning unit led to the dripping, it said.
It said after receiving complaints, it instructed staff to assist passengers, quickly resolve the issue and clean the car floor so that the service was not halted.
Passengers on a Cat Linh - Ha Dong metro trainuse umbrellas to take shelter from water leak, May 19, 2025. Video by NT
The train was later sent to the Phu Luong depot for inspection and repairs.
Technical experts have been called in to resolve the issue by Tuesday.
The Hanoi Metro noted that the trains and technical systems were manufactured and delivered in 2017.
"This rare and unfortunate incident of water leakage from the air conditioning system, which caused inconvenience and hygiene concerns for passengers in one car, is regrettable. We sincerely apologize to our passengers."
In February, the Cat Linh – Ha Dong line suffered a service disruption due to a power outage, and passengers were refunded and advised to seek other transport means.
The 13-kilometer elevated line was inaugurated in 2021 with 12 stations.
Each train has four cars that can carry up to 960 passengers.