KUALA LUMPUR: An initial investigation by the Malaysian Fire and Rescue Department (JBPM) revealed that the fire at Tenaga Nasional Berhad's (TNB) main substation at Mid Valley Megamall this morning was probably caused by overheated cooling oil.

Kuala Lumpur JPBM Operations Unit assistant director M Fatta M Amin said the oil, which can withstand heat up to 137 degrees Celsius, is used to cool cables at the substation and not for power generation.

"However, it is believed that the substation was excessively hot and suddenly started burning," he told reporters at the scene.

According to him, there were four TNB substations in the Mid Valley building, but only one was on fire, while the other three were unaffected.

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

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

"However, the police are still waiting for further investigations by JBPM forensic experts," he said when met at the scene.

Earlier today, several videos went viral on social media showing a black plume of smoke from the building at around 10.30 am.