At least 20 people have died and more than 100 injured after wildfires tore through woodland and villages around Athens, as Greek authorities rushed to evacuate residents and tourists stranded on beaches in coastal areas early Tuesday.

The majority of victims were found in their homes or cars in the seaside resort of Mati, 40 kilometres (25 miles) northeast of the capital, government spokesman Dimitris Tzanakopoulos said.

Eleven people were seriously injured, he added, while 16 of those injured were children.

Late Monday, an AFP photographer came across a burned out car and motorcycle with four charred bodies underneath them near the port town of Rafina, one of the worst affected areas about 40 kilometres east of Athens.

Authorities were trying to evacuate inhabitants, Tzanakopoulos said, while searches for further victims continued.

Nine coastal patrol boats, two military vessels and "dozens of private boats" assisted by army helicopters were mobilised to help those stuck in Rafina harbour.

Evacuees were transferred to hotels and military camps, while worried relatives flocked to the area.

Police in the town earlier said they found two Danish tourists out of a group of 10 in a boat at sea off the town and were trying to locate the others.

Civil protection chief Yannis Kapakis said he had told Prime Minister Alexis Tsipras, who cut short a visit to Bosnia to return home, that winds up to 100 kilometres an hour were creating "an extreme situation."

In the north of the country, more than 300 firefighters, five aircraft and two helicopters were mobilised to tackle the "extremely difficult" situation, Athens fire chief Achille Tzouvaras said.

The Greek government invoked European Union civil protection agreements to seek help from its EU peers, with the country tinder box dry and at risk of more fires. Blazes have caused widespread damage in Sweden and other northern European nations.

Video footage showed inhabitants fleeing the fires by car, with several buildings and homes damaged, as the region of Attica -- where Athens is situated -- declared a state of emergency.

"If I hadn't left, I'd have been burned," a 67-year-old resident who gave her name as Maria told AFP.

Near the town of Marathon, several residents fled to safety along the beach, while some 600 children were evacuated from holiday camps in the area.

Tsipras said "all emergency forces have been mobilised" to battle fires along at least three fronts.

Emergency services were banking on a drop in the wind but the forecast for the region -- which has experienced temperatures topping 40 Celsius (104 Fahrenheit) -- suggest conditions would remain challenging into Tuesday.

Smoke from the blazes blotted out the sun over the famed Parthenon temple in Athens, where some ministries closed Monday afternoon due to the soaring heat.

"I am really concerned by the parallel outbreak of these fires," Tsipras said, with officials raising the possibility they could have been started deliberately by criminals out to ransack abandoned homes.

Fires are a common problem in Greece during the searing heat of the summer and can be major killers.

Fires in 2007 on the southern island of Evia claimed 77 lives.