Charred bodies were found in "cars, houses and in fields" in the area surrounding the village of Zacharo, in the southwest Peloponnese, firefighters said.
"It's a Biblical catastrophe, the sight is horrible. I saw people burnt alive in their cars," Christos Kafiras, the prefect of the Ilia fire department, told a television channel on Friday.
Throughout Friday and into the night, more than 170 fires raged across the country, from the western Ionian islands to Ioannina in northwestern Greece and down to the south.
With at least 25 fires starting long after dark, including one in a park in a wealthy neighborhood of Athens, authorities warned on Saturday that more blazes were expected.
A recent three-day heat wave, in which temperatures have touched 40C, has left forests and shrub land parched, with flames fanned by the strong winds.
But some of the fires are thought to have been started by arsonists.
Nicole Itano, a journalist in Athens, told Al Jazeera: "There is a lot of suspicion that these fires and previous fires from the summer have been set by arsonists. The suspicion is that people are setting fires in order to clear land for new developments."
But she said: "People here are simply stunned by the sheer number of the fires."
She said that gale force winds had made it difficult for firefighters, adding that "even without those winds I think firefighters would have been hard pressed to deal with them simply because there are so many".
Itano also said that the government had come under criticism for not being prepared despite "knowing this was going to be a long, hot, dry summer".
"The mood in Greece is definitely one of anger and this may affect the ruling party as they go into elections," she said.
Greece is expecting to see early elections in September.
In Athens, the capital, a fire broke out during the night in a park in the Filothei area, a few kilometres north of the city centre.
Two forest fires, that broke out near the Greek capital, blocked off the main highway between Athens and its international airport, authorities said on Saturday.
|High winds have hampered efforts |
to control the blazes [AFP]
"The motorway has been shut down," a fire department spokesman said. Karolos Papoulias, the Greek president, said: "We are in a state of national mourning ... We must do whatever is necessary so this does not happen again."
Costas Karamanlis, the country's prime minister, held a crisis meeting in Sparta, in the southern Peloponnese.
After touring the fire-ravaged area the day before, the prime minister called the situation "a national tragedy."
The government has appealed to European Union countries to "send any help they can," said Spyros Flogaitis, the acting interior minister, after an emergency meeting of Greece's civil protection authority.
The Greek military has been called in to help firefighters.
Residents and local officials called television stations with desperate appeals for help.
"I'm one person, all alone in the dark in a blazing valley. I need help," said one man, whom the Mega television channel said was the mayor of Palaiochori village.
One woman in the village of Rodina, near Zaharo, told Antenna television that about 20 people, including children, were trapped in the village.
"We can see the fire in front of us. It's at our feet," said the woman, who did not give her name. "We're choking on the smoke."