CLP later said power supply had resumed at 12.11am.

The affected buildings included Lung Kwong House, Lower Wong Tai Sin Estate, Mei Tak House in Mei Tung Estate and the private Lions Rise development.

Facebook users earlier reported blackouts also hit part of Wong Tai Sin Shopping Centre.

The Environment and Ecology Bureau expressed concern about the outage.

“The government is very concerned about the electrical incident that happened in Wong Tai Sin tonight, leading to a power supply outage in some buildings. Residents were trapped in lifts and might have an uncomfortable night under this hot weather,” the bureau said.

It added it had urged CLP Power to expedite the repairs, and the power company had provided temporary generators in an effort to restore power to some affected residences.

A government spokesman earlier said four cases of lift shutdowns were reported from around 8pm to 9.19pm, covering residential and industrial blocks and a shopping centre in the area.

Images circulating online show shoppers walking inside a mall during the blackout, while other pictures depict residential blocks without electricity, leaving all flats in darkness.

Online users said there was a momentary flicker of lights at 8.20pm, while others reported experiencing a sudden loss of electricity in their entire building.

Police said officers were deployed to direct traffic on Tung Tsing Road after all traffic lights stopped working at 8.15pm.

Lawmaker Ngan Man-yu of the Kowloon East geographical constituency said many buildings were affected, with residents standing around on the streets not knowing when the power supply would resume.

Some residents from the higher levels of a block at Lower Wong Tai Sin Estate chose to stay on the street for the cooler air and avoid climbing the stairs to their flats after the outage.

The temperature remained at about 29 degrees Celsius (84 Fahrenheit) at night, with the relative humidity lingering at around 85 per cent.

The Home Affairs Department said temporary shelters at Tung Tau Community Centre and Wong Tai Sin Community Centre were opened to residents in need.

It added the Wong Tai Sin District Office would closely monitor the situation, and liaise with other government departments to provide residents with appropriate help.

“CLP staff tried to locate the affected buildings and supply power by using temporary electricity generators. And they told me it could be fixed hopefully by midnight,” Ngan said.

“I also told them to post notices outside the affected buildings to let people know the status instead of them purposelessly waiting on the streets.”

Members of the Lung Ha subdistrict care team were deployed to help affected residents.

The government urged CLP Power to expedite repairs, and the utility had provided temporary generators in an effort to restore power to some affected residences. It also reminded the company to provide regular updates on the progress of repairs to keep residents informed.

CLP Power, which supplies Kowloon, the New Territories and most outlying islands, logged five supply disruptions in the first four months of this year, including three voltage dip incidents that left more than 200 residents trapped in lifts.

An existing penalty mechanism for outages requires electricity providers to pay fines based on the duration of the incident and the number of people affected.

The policy was among measures announced in December following the government’s interim review of its “scheme of control” agreements with the city’s two suppliers, CLP Power and HK Electric.

Under the mechanism, CLP Power 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.

Both companies can receive a 0.015 per cent incentive if they restore the supply within 65 minutes of an outage and maintain a yearly average reliability rate of 99.996 per cent or above.

The next interim review for the two energy firms will take place in 2028.

Lawmaker Michael Tien Puk-sun reiterated CLP Power needed to provide help to install lift voltage dip mitigation devices in old buildings, given the blackout caused entrapments this time.

“The devices also serve as a backup battery. Once it is triggered, it will utilise the backup power to bring the lift to the nearest floor and open the door,” Tien said. “It will work regardless if there is a power disruption or a voltage dip.”

The city has 73,000 lifts but only 22,000 are fitted with such devices allowing them to resume operations after self-inspection.

The Electrical and Mechanical Services Department said last month that such a device installed in old buildings cost more than HK$500,000. But Tien argued these devices did not cost that much after his conversation with industry leaders.