CLP and the government came under criticism at the Legislative Council on Friday over their supervision of power supply contingency infrastructure, after it was revealed that a backup feeder for New Territories West had stopped working months before a cable bridge fire plunged about 175,000 households into darkness in June.

During a special Legco meeting to discuss the incident, CLP officials told lawmakers that a fluorescent light that caught fire on the cable bridge in Yuen Long was the most probably cause for the massive blaze.

Workers had to manually restore power that night as the fire also damaged communication cables to one of two backup systems.

A managing director for CLP, Chiang Tung-keung, admitted that the other backup system had malfunctioned months before the blaze because one of the cables, that was routed through the mainland, was damaged.

"A few months before the incident, because of construction work, the backup power supply malfunctioned and since then the CLP has been discussing with the relevant parties on repair matters," Chiang explained.

"Unfortunately on the night in question, the backup set was not repaired."

Government officials, for their part, said they were unaware of the cable damage because part of it was outside Hong Kong and their jurisdiction.

They added that the cable has since been repaired.

"The damage to the cable happened outside Hong Kong and because of that it took longer for CLP to negotiate with the other side and originally that shouldn't pose a problem because it was supposed to be a backup source but it so happened that there was this major fire," said Secretary for Environment and Ecology, Tse Chin-wan.

New Territories North lawmaker Gary Zhang said he was disappointed by the officials' answers.

"They're supposed to have a very good understanding of what actually happened in our power supply network," he told RTHK.

"I think with the backup system, we could have restored the power supply much earlier."

Roundtable lawmaker Michael Tien, meanwhile, urged the authorities to set up another backup system with infrastructure that's fully within Hong Kong.