Athens: A forest fire near the Greek capital forced power networks to shut down on Wednesday, causing blackouts, fire officials said.

At least 20 fire engines, scores of firefighters, three helicopters and eight fire-fighting planes were battling the blaze, about 20 kilometres southeast of Athens.

"It is a very difficult operation as the front is very wide and winds are strong," said a fire official who declined to be named.

Rescue services were called in to rescue dozens of people trapped in elevators after electric pylons near the blaze were automatically shut down.

"Coastal suburbs and the centre of Athens were affected after power lines ... were forced offline," an official from electricity utility Public Power Corporation said.

Firefighters were working to prevent the fire from spreading to the main international airport, but airport officials said no flights had been affected so far.

Last year, wildfires swept through villages in southern Greece during a ten-day inferno that killed at least sixty-five people and devastated the local economy.