The Electrical and Mechanical Services Department on Monday gave CLP Power four weeks to submit a report on a voltage dip yesterday, that led to people being trapped in lifts and firefighters being called in to conduct rescue operations.

Authorities said the incident, which affected Tsuen Wan, Kwai Chung, and Tsing Yi, happened at around 3.15 pm, with the police having received multiple reports of the sound of an explosion at a CLP substation in Tsing Yi.

The government said CLP reported the incident to the Electrical and Mechanical Services Department around 15 minutes later, in accordance with an established mechanism. It said, according to CLP's report, a fault had occurred at its Nga Ying Chau Street substation with an automatic protection system immediately kicking in to isolate the faulty part.

CLP said the incident hadn't resulted in an electricity shortage but it did lead to short voltage dips, which might have left some customers experiencing dimming or flickering lights. It also said some electrical installations, like lifts, might have stopped working because their protection systems had been activated.

In addition to asking for a detailed report from CLP, the department called on the power company to take follow up and improvement measures, saying it would monitor the repair work.