Padang/Pekanbaru. A massive blackout swept across Sumatra island on Friday evening after a major disruption in the regional power transmission system, leaving millions of residents without electricity and crippling traffic and public activity in several provinces.

The outage affected wide areas across Aceh, North Sumatra, West Sumatra, Riau and parts of central Sumatra after disturbances hit the island’s interconnected electricity network at around 6:44 p.m. local time, according to state utility PLN.

PLN serves around 4.4 million customers in North Sumatra, 2.6 million in Riau, 1.96 million in West Sumatra and 1.7 million in Aceh.

Preliminary information indicated the disruption began when the Northern Sumatra and Central Sumatra power systems became disconnected, triggering a total blackout across parts of northern Sumatra. The disturbance was linked to the 275-kilovolt transmission line connecting Rumbai and Muaro Bungo, which disrupted electricity distribution across multiple provinces.

PLN said hundreds of personnel had been deployed to accelerate recovery efforts while technicians conducted a comprehensive inspection of the transmission and power systems.

“We are continuing to coordinate with teams on the ground to determine the cause of the disruption,” PLN Aceh communications manager Lukman Hakim said in Banda Aceh on Friday.

The blackout plunged major cities into darkness and disrupted public services and economic activity across the island. In Pekanbaru, the capital of Riau province, traffic congestion worsened after traffic lights stopped functioning during the evening rush hour.

Similar scenes were reported in Padang, the capital of West Sumatra, where motorists were forced to navigate intersections without functioning signals, causing gridlock along several major roads.

Small businesses were also affected by the sudden outage. Food vendors and shop owners said they were forced to rely on candles and mobile phone flashlights for lighting, while some businesses closed earlier than usual because of the disruption.

PLN apologized for the outage and urged residents to remain calm as restoration work continued.

Gregorius Adi Trianto, executive vice president for corporate communications at PLN, said technical teams had been dispatched across the affected regions to restore electricity and investigate the root cause of the system failure.

The utility said updates on recovery efforts would be provided through the PLN Mobile application and its customer service hotline.