At least 79 people died in huge wildfires around Athens, Greek authorities said yesterday, as rescuers scoured scorched homes and burned-out cars for survivors of one of the deadliest fire outbreaks in Europe's modern history.

Scores of locals and holidaymakers fled to the sea to try to escape the flames as they tore through towns near Athens stoked by 100-kilometre-per-hour wind gusts, devouring woodland and hundreds of buildings.

Greek media have described the disaster as a "national tragedy", while Prime Minister Alexis Tsipras cut short a visit to Bosnia and announced three days of national mourning.

A fire service official said that searches to find those missing in the fires continued yesterday, although there was still no official word on the number of people unaccounted for.

Spokeswoman Stavroula Maliri said authorities knew of "79 dead", surpassing the 77 people killed in the previous deadliest fires in Greece, on the southern island of Evia in 2007.

"We've received numerous calls reporting people missing," Maliri said.

When the fires broke out on Monday evening, terrified residents and tourists were overtaken by the flames in homes, on foot or in their cars.