Kuala Lumpur fire and rescue department assistant operations director Fatta Amin said the oil, which could withstand heat up to 137 degrees Celsius, was used to cool cables at the substation.

“However, it is believed that the substation overheated and caught fire,” he told reporters at the scene.

Fatta said there were four TNB substations in Mid Valley, but only one caught fire. The remaining three were unaffected.

He said all of the substations were capable of supplying power within a 10km-radius of Mid Valley Megamall.

Meanwhile, Brickfields police chief Amihizam Abdul Shukor said preliminary investigations found no elements of mischief in the incident.

“However, the police are still waiting for further investigations by forensic experts from the fire and rescue department,” he said.

Earlier, it was reported that a fire started at a TNB substation room inside the mall, with an estimated 70% of the 40mx40m room damaged in the blaze. No casualties were reported.