But it did not explain what had happened to cause the disruption and said its investigation continued.

Tse Chin-wan, the secretary for environment and ecology, said the firm “should not wait” to upgrade its system in Kowloon and the New Territories until a review of incidents over the past three years was completed within the next 12 months.

He was speaking after a 400kV overhead line linking Yuen Long to Shenzhen suffered a drop in voltage just before 3am, which caused power cuts and other glitches in Kowloon and the New Territories.

The incident is thought to be connected to thunderstorms in the area at the time.

Tse said the company should “enhance the capability of the power supply system, particularly the lightning protection capability of 400kV overhead line towers, as soon as possible to withstand the impact of inclement weather”.

He added that the Electrical and Mechanical Services Department had asked the company to step up protection against lightning to minimise the risk of power cuts caused by potential frequent thunderstorms over the next few months.

Tse said the power firm also needed to identify the cause of the incident as soon as possible, draw up improvement plans and submit a report to the department within four weeks.

The company apologised for the inconvenience to residents in “individual buildings” hours after the latest incident and blamed bad weather for the problem.

“A thunderstorm warning was in force when the voltage dip occurred,” a spokesman said. “It is suspected that the 400kV overhead power supply system might have been impacted by the unstable weather conditions.”

Fung Chuen Court in Kowloon’s Diamond Hill was among the buildings that suffered blackouts, and a resident went to the lobby to seek help after his flat lost power. The supply was not restored for an hour.

CLP Power said it had sent engineers to the area to carry out inspections and they were told the affected buildings had arranged for electricians to restart the equipment and restore the electricity supply.

Ho Wing-yip, a veteran electrical and building services engineer, said voltage dips could become more frequent as climate change was causing more extreme weather events. He added that the last voltage dip happened in Tuen Mun two months ago.

Ho said CLP Power had installed protection at some transmission towers to minimise the possibility of damage from lightning strikes, but they were insufficient.

He urged the company to make the installation of protection at transmission towers in elevated areas a priority, as well as at 400kV power supply systems, which served large numbers of customers.

Ho said the utility could restore electricity in a short time, but a voltage dip might cause blackouts in buildings that were more sensitive to the power supply. It could take one to two hours for contractors to restore the supply, he said.

“The power supplier has to do something as it is difficult to predict how many customers will be affected by voltage dips. It could be massive,” Ho said. “The most worrying part is that the elderly and patients with medical equipment could be affected.”

He added CLP Power should be held responsible if it failed to maintain its network properly and allowed voltage dips, but that it should not be blamed if the incident was caused by natural factors.

Edward Lau Kwok-fan, the chairman of the Legislative Council’s environmental affairs panel, said the company should review its management and consider compensation for affected customers.

“A stable electricity supply has been one of the government’s indicators for assessing power companies’ performance,” he added.

“Voltage dips definitely affect the indicator. The government and CLP should discuss a compensation mechanism as soon as possible.”

Lau said the city should consider running power lines underground in future to reduce the risk of damage caused by weather.

CLP Power managing director Joseph Law Ka-chun stressed on Sunday night that the company would strive to improve the resilience of its grid to extreme weather and to shorten the time taken to restore the supply if there were incidents.

He said frequent extreme weather conditions posed problems for the company.

Law added the company would introduce short, medium and long-term measures to tackle incidents and restore power as fast as possible.

He said the inspection system at key facilities would be improved using human resources and technology.

Additional resources, such as mobile power generation vehicles, would be deployed in the event of power cuts.

Measures would be taken over the medium term to boost protection for outdoor equipment, with added measures against lightning and extra anti-flooding work around low-lying facilities.

Major reviews of asset management and maintenance would be carried out in collaboration with the government as part of the long-term measures.