Hundreds of people were evacuated on Sunday as firefighters backed by water-bombing aircraft waged a titanic battle to contain a raging wildfire in Athens' eastern suburbs.

The inferno forced people to flee their homes while authorities evacuated patients from two childrens' hospitals, a summer camp and a retirement home as flames and smoke threatened outlying residential districts.

Many home-owners were defying the pleas of local officials to leave and were staying behind to fight the inferno -- the worst since wildfires in 2007 that claimed 77 lives -- amid power and water supply cuts.

"Our house was spared yesterday but today the fire returned," said Theofania Kassimati, a 53-year-old resident of the eastern residential suburb of Dionysos, who was forced to flee.

"People were going around with loudspeakers urging us to leave, so we packed a few things and our little dog and left," she said.

Among those who stayed behind was a Koukounari man who doused dry brush with a watering hose as he told state television: "We fought this fire and saved our homes alone."

"The firemen told us to evacuate to avoid getting trapped, and then they left," he said.

Nearly 600 firefighters, hampered by strong winds and thick smoke, were struggling to halt the wildfire two days after it started Friday despite assistance from a fleet of 12 water-bombing planes and seven helicopters.

"Weather conditions do not permit the aircraft to operate as they would want and many smouldering areas are left behind," Athens prefect Yiannis Sgouros told state television NET.

The residential suburbs of Agios Stafanos, Anthousa, Gerakas and Pallini were most at risk from the blaze, which was being fanned Sunday by strong winds. Residents of a psychiatric clinic had to be taken to safety.

Patients at the Penteli military hospital were evacuated on Sunday as a precaution and the merchant marine ministry said coastguard vessels were on standby to transport any residents trapped in coastal areas.

Two people were admitted to hospital, one with burns and the other with a heart-related problem, state television NET reported.

The fire department said a "gigantic mobilisation" was underway and that 85 blazes had erupted nationwide in the past 24 hours.

Around 12,000 hectares (30,000 acres) of land are believed to have been destroyed according to officials' early estimates, and the blaze is feared to have destroyed or damaged scores of rural and summer homes.

Prime Minister Costas Karamanlis called an emergency government meeting after overflying the scorched area in a helicopter and President Karolos Papoulias hastened back from vacation.

Karamanlis said the country faced "a great ordeal" and praised the "superhuman" effort of firefighters.

The fire started late on Friday in the rural area of Grammatiko around 40 kilometres (25 miles) northeast of Athens that has been earmarked for a new waste disposal facility strongly opposed by local residents.

Strong winds on Saturday pushed it back and forth across a forested area dotted with villages.

Firebreaks in the forest on Mount Penteli, the last barrier to the capital, failed to hold the flames late on Saturday when fire-fighting aircraft were withdrawn for the night.

"This is a very significant environmental disaster, perhaps the gravest in recent years," the prefect of the greater eastern Athens area, Leonidas Kouris, told ANT1 television.

The European Commission on Sunday said it had activated the European Union's civil protection process to help Greece, notably requesting fire-fighting planes from Italy to join Greek efforts.

"Due to the extreme weather conditions and severe forest fires Greece Saturday evening activated the Community Mechanism for Civil Protection and requested assistance with aerial means," it said.

The wildfire also continued to burn north of Marathon, the main source of Athens' water supply, and led authorities on Saturday to relocate missiles and ammunition from a military camp.

With temperatures frequently running above 40 degrees Celsius (104 Fahrenheit) and seasonal strong winds, Greece is particularly vulnerable to summer fires that ravage forest and agricultural land.

Other fires burned in the central Greek region of Viotia, on the Aegean islands of Skyros and Evia, the Ionian island of Zakynthos and in the Peloponnese peninsula.