A power blackout hit the Greek capital and parts of southern Greece around noon on Monday, just a month before the start of the Athens Olympic Games, but officials said services were gradually being restored.
Trains, the metro system and lifts ground to a halt across the city and traffic lights went out briefly in some of the main road networks.
"There was a significant problem in the Lavrion power station which caused failures in the southern network of the country. This affected the Cyclades islands, the Peloponnese and the greater Athens area," Ministry of State spokesman Panos Livadas said.
"Olympic venues and hospitals faced no problems as they have their own generators".
Management of electricity utility PPC were not immediately available for comment.
Livadas said power was being restored in the Athens region by limiting supply to some areas of the countryside.
The main electricity network may have crashed because of a surge in air conditioner use during a heatwave over the last few days, local media said.
A spokesman for the Athens Metro said some trains were stranded inside tunnels. "Doors have been opened and people are being led out on security walkways by drivers and station masters."
A suburban railways spokesman said two trains had also stopped in mid-journey and passengers had to walk to the next station.
Fire services reported receiving more than 400 calls in five minutes from people trapped in lifts across the city.
