At least 50 people have died and more than 100 injured after wildfires tore through woodland and villages around Athens, AFP reported Monday night.
Greek authorities are rushing to evacuate residents and tourists stranded on beaches in coastal areas, according to the report.
The majority of victims were found in their homes or cars in the seaside resort of Mati, located 40 kilometers (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.
Nine coastal patrol boats, two military vessels and "dozens of private boats" assisted by army helicopters were mobilized to help those stuck in Rafina harbor, according to AFP.
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.
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.
Greek Prime Minister Alexis Tsipras said "all emergency forces have been mobilized" to battle fires along at least three fronts.
Fires are a common problem in Greece during the heat of the summer and can be major killers.
Fires in 2007 on the southern island of Evia claimed 77 lives.