“This incident should not be treated as an isolated event,” Secretary for Environment and Ecology Tse Chin-wan said during his meeting with company managing director Joseph Law Ka-chun.

“Recently, there have been a number of voltage dips and power supply interruption incidents, and the frequency of these incidents has led to concerns about whether CLP’s service quality is on the decline.”

Tse stressed the city could only maintain “the stable and reliable power supply that Hong Kong has always been proud of” by reducing the recurrence of similar incidents.

The company said it was carrying out a detailed investigation into the cause of the blackout and that it would submit a report to authorities.

“CLP Power apologises again for the inconvenience caused to customers who were affected by the incident,” a spokesman said. “CLP Power appreciates the concern of the Environment and Ecology Bureau regarding recent power incidents and the public expectation for a reliable power supply.”

He added the company was committed to “keeping pace with the times and adopting practical measures” to continuously maintain a reliable power supply.

In addition to reviewing power cuts over the past three years, Tse demanded the company list the causes of the disruptions, improvement measures, the status of implementing the steps and their expected effectiveness.

The Electrical and Mechanical Services Department would also help hire an independent consultant for the inquiry, he added.

The inspection would include a review of the safety design of the power supply system, including its ability to withstand external factors, and the company’s repair and preventive maintenance arrangements, as well as its procurement policies and qualification of staff.

The department would establish a task force with CLP Power to complete the work and submit a second report within 12 months, Tse said.

“The director of electrical and mechanical services will also invite local experts and scholars to establish a steering committee to work together in supervising the work of the independent consultant and advise on the report,” he said.

The electricity firm said on Wednesday night that a fault in an 11kV cable triggered the outage, with four reports of people trapped in lifts.

The power outage began during the peak dinner hour at 8.02pm on Wednesday and lasted until 12.11am the following day, with the area affected ranging from the Lions Rise private housing complex in Wong Tai Sin to Mei Tung Estate in Kowloon City.

A Chinese restaurant was said to have lost at least HK$10,000 (US$1,280) due to spoiled food and customers leaving without paying.

The manager of Chinese restaurant Hakka Bistro said some customers apparently “took advantage of the chaos” and left without paying.

“All 30 or so tables were fully occupied [at the time],” she said.

In the same shopping centre, a server at Japanese restaurant Karayama said her eatery was packed during the blackout. She added that some customers managed to continue their meals after turning on their phone flashlights and that all paid before leaving.

The power at Lung Kwong House, a public housing block near Wong Tai Sin MTR station, did not come back on until 12.30am, according to residents.

Wong Tai Sin resident Nero Kwong, 40, said he was having dinner with his family at home when all his electrical appliances shut down.

“There was suddenly a ‘boom’ sound,” he said.

They decided to go downstairs because their home was getting too hot and they waited past midnight before returning home, he added.

Maggie Wong, 48, said she was jogging when the blackout started, so she was only aware of the incident when she returned home.

“The experience was terrible when you could not get a shower after a jog,” she said.

CLP Power, which supplies electricity to Kowloon, the New Territories and most of the city’s outlying islands, must pay a fine of HK$20 million (US$2.56 million) or a deduction of 0.015 per cent from its permitted return if it records 15 million minutes of power disruptions in a year.

HK Electric, which supplies Hong Kong and Lamma islands, also faces a fine of HK$20 million if it has 10 million minutes of outages in a year.

The blackout on Wednesday lasted about 540,000 minutes.

CLP Power has reported six power disruptions in the first half of this year, including a fire at a substation in Tsing Yi that resulted in at least 20 lift entrapment cases.

Lawmaker Edward Lau Kwok-fan urged CLP Power to compensate affected residents, even though it would not be subject to any punishments under the current agreement with the government.

“Many residents were affected,” Lau, who chairs the Legislative Council’s panel on environmental affairs, said in a radio interview. “It is unreasonable for the power company not to be penalised or to compensate for a four-hour blackout.”

He also suggested authorities review the current incentive-punishment system and penalise power utilities according to the degree of blameworthiness in each incident.

Last month, environment authorities proposed an extra penalty charge for CLP in cases of power dips.