Istanbul (CNN) -- A major power blackout hit Turkey's largest city Saturday afternoon, leaving millions of residents without electricity while shutting down Istanbul's subway and tram systems.
Officials with the Istanbul governor's emergency situation directorate told CNN the massive outage appeared to be caused by a failure on a main power transfer line running from the Western city of Bursa.
"There was no power in all of Istanbul," one official said. Another added, "We think there was also no power in Izmit and Adapazari," referring to two other cities in western Turkey.
Istanbul is Turkey's cultural and commercial hub, with a population of more than 12 million people.
The sparkling lights along Istanbul's main pedestrian thoroughfare, Istiklal Caddesi, went completely dark as snow began falling on the city.
In subway stations, lights were on in the tunnels but escalators stopped operating. Meanwhile, a message repeated over the loudspeaker system announcing "due to a technical problem the metro is not running."
The blackout reached from the neighborhoods of Istinye to Atakoy, a distance of around 20 kilometers.
After at least an hour of darkness, residents reported some power returned to the neighborhood of Kadikoy on the eastern side of Istanbul.