Debris collapsed into a power distribution tunnel at Tal-Qroqq on Thursday, causing considerable damage to the distribution system, Enemalta said.
Several stones fell into the distribution tunnel as a result of works on a site at the University of Malta in Tal-Qroqq.
"This damage has affected connectivity between Mosta and Kappara distribution centres and other links supplying the Sta Venera area," the company said.
Enemalta said that thanks to automated systems and control facilities, the damage had minimal impact on the power supply.
It warned that there may be short power interruptions while repairs are made but every effort will be made to limit inconvenience.
A magisterial inquiry has been appointed.
Damage affects Mater Dei Hospital airconditioning
The damage to the distribution system affected Mater Dei Hospital, where airconditioners in several wards were turned off and staff could be seen taking in fans.
The hospital in a post on its Facebook page apologised for the inconvenience.