A massive power cut caused chaos Tuesday across Turkey, shutting down the metro networks in Istanbul and the capital Ankara, with the government saying an outside attack on the system was not ruled out.

The power cut, the worst in one-and-a-half decades, began around 10:36 am (0736 GMT) in Istanbul, the state-run Anatolia news agency quoted the Turkey Electricity Transmission Company (TEIAS) as saying.

It also hit almost all the country's provinces from the Greek border to the southeast.

"Every possibility including a terrorist attack is being investigated," in the outage affecting the country of some 76 million, Prime Minister Ahmet Davutoglu said.

He added that a crisis desk was established at the energy ministry.

Energy Minister Taner Yildiz also said the authorities were investigating whether the power outage was due to a technical failure or a "cyber-attack."

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

The ministry was quoted as saying by Turkish media that a power cut on this scale had not been seen in 15 years.

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

The blackout trapped people in elevators in Istanbul and rescue teams rushed to subway stations to evacuate stranded travellers.

Traffic lights also were not working in several places in the city, causing huge traffic jams, with officers taking to the streets in an attempt to break the logjams.

Websites warned commuters to take special care of traffic accidents.

The Istanbul tramway which links outlying areas with the historic touristic heart of the city was also down, as was the metro in the Aegean city of Izmir.

In the heavily industrialised western city Izmit, near Istanbul, the cuts prevented many factories and workshops from 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 between Europe and said it could take hours before the power cut was restored.

The Chamber of Electrical Engineers of Turkey however claimed that it happened because some private power suppliers had refused to sell electricity due to low prices.

The DHA news agency said almost all provinces in Turkey were affected by the outage, except the Van province in the east which imports electricity from neighbouring Iran.