The death toll from the wildfire that ripped through a Greek resort town near Athens has reached at least 81 as frantic relatives and officials began the grim task of identifying bodies.

Hundreds of people were trapped in the eastern resort of Mati on Tuesday morning (AEST) as flames whipped around them.

Many jumped into the sea to survive, but others died from suffocation, either in their cars or trapped on the edge of steep cliffs.

More than 280 firefighters were still in the area to the northeast of Athens in the wider Rafina area, dousing the remaining flames to prevent flare-ups.

A further 200 firefighters backed up by a water-dropping helicopter were tackling the second forest fire west of the capital, near Agioi Theodori, where local authorities pre-emptively evacuated three communities, a children’s summer camp and three monasteries overnight.

Flags across Greece flew at half-mast after Prime Minister Alexis Tsipras declared three days of national mourning.

The Greek anti-terrorist service was investigating suggestions that the blaze – one of several throughout the Attica region – was started deliberately, a security source said.

Arson is often thought to be behind some fires in a crude attempt to clear forest land for building.

The fire brigade said the death in hospital of one person who had initially survived brought the toll up to 81.

The service had also received dozens of calls reporting missing people, but it was unclear if some of them were among those already found dead, a spokesperson said.

Some people appeared on television to plead for help.

“I’m looking for my mum,” a young woman told Greece’s SKAI TV between sobs.

The fire broke out on Monday at 4.57pm, an hour which is observed as a siesta time in rural Greek communities. Mati was popular with local tourists, including pensioners.

Rescue teams combed through the area and the sea on Wednesday trying to locate anything which could offer clarity on the missing, who are thought to number about 40.

“We took our cars and went down to the sea and got into the sea to escape, but there were people who did not make it,” Mati resident Agni Gantona said.

“We got into the water and stayed there for about five hours until the boats came to pick us up. We were at the beach with about 250, 300 people.

“Some were burned, some were near fainting from the smoke and the flames. Groups of us, we were holding each other by the hand and shouting each other’s names, because we could not see from the smoke.”

“Armageddon,” wrote the daily newspaper Ethnos on its front page.

It carried a photo of a burned Greek flag hanging among the branches of a charred tree.

-with AAP