A massive power outage caused chaos across Turkey on Tuesday, shutting down the subway networks in Istanbul and the capital of Ankara, with the government not ruling out an outside attack on the system.

The outage, the worst for 15 years to affect the country of around 76 million people, began at 10:36 am (3:36 pm China time) in Istanbul, the Anatolia News Agency quoted the Turkey Electricity Transmission Co as saying.

It also affected nearly all the country's provinces from the Greek border to the southeast.

"Every possibility, including a terrorist attack, is being investigated," Prime Minister Ahmet Davutoglu said.

Energy Minister Taner Yildiz said the authorities are investigating whether the outage was caused by a technical failure or a cyberattack.

"The most important thing for us is to bring the system back to life. This is not something we frequently experience," he said.

Media reports said the power cut affected at least two dozen cities, where telephone and Internet lines were also mostly down.

People were trapped in elevators in Istanbul and rescue teams had to evacuate stranded subway travelers. Traffic lights were out of action in several places, causing huge traffic jams. All health services at hospitals, including surgeries, also were stopped.

The Istanbul tramway, which links outlying areas with the historic heart of the city, was also out of action.

Subway service in the Aegean city of Izmir was halted, while many factories in the industrial western city of Izmit stopped functioning.

There were conflicting initial reports about the cause of the outage, but Turkish grid operator TEIAS said it resulted from a severing of the power lines from Europe, adding that it could take hours before power was restored.

However, the Chamber of Electrical Engineers of Turkey said the outage occurred because some private power suppliers had refused to sell electricity due to low prices.

(China Daily 04/01/2015 page1)