A team of firefighters wearing breathing apparatus and carrying heavy equipment had to run about 2km to reach the burning train in the Tai Lam Tunnel.
The 20 firefighters from Tsuen Wan fire station - lugging ladders, extinguishers, fire hoses and crowbars - ran down four floors of an emergency entrance to the railway line before continuing for about 10 more minutes inside the tunnel.
When they arrived, a transformer was still ablaze on the roof of the second-last carriage of the seven-carriage train, New Territories South divisional officer Man Shu-bor said.
'The train driver tried to fight the blaze with a number of extinguishers but the train was too high and he was unable to reach and spray the source of the fire,' Mr Man said.
Once the KCRC disconnected power to the train, firemen climbed on to the roof and took about 10 minutes to douse the flames with a water jet and five extinguishers.
'The main difficulty was that the fire scene was far from the Chai Wan Kok Street emergency access point in Tsuen Wan. Our colleagues carrying equipment had to run for 2km to reach it before we started fighting the blaze,' Mr Man said.