The fire broke out on the vessel near Stonecutters Island on Wednesday evening and was finally put out around 15 hours later.
The Fire Services Department said it was still investigating the cause of the fire, adding that more than 30 fire trucks, nine fireboats and almost 200 firemen and rescue workers had been deployed to the scene.
No one was injured in the blaze.
Commander Yiu Men-yeung from the department’s marine and diving division said the 100-metre barge was carrying over 3,000 tonnes of scrap metal, which made the operation extremely challenging.
“Because there was a lot of scrap metal stocked up on the vessel, just like a mountain… our water and fire extinguishing foam could not reach the source of the blaze directly, which made our work more difficult,” the commander said.
Yiu added that a malfunctioning water pump on the vessel, coupled with strong winds and high waves, made it even more difficult for firefighters to control the flames.
The department had earlier warned residents in West Kowloon and Tsing Yi to close their doors and windows because of the acrid smoke coming from the blaze.
But Yiu said officials did not receive any reports of people feeling unwell.