Eighteen bodies have been found in a forested area of northern Greece hit by wildfires for the past four days, the Greek fire service says.
Initial reports suggest those who died may have been migrants. A coroner and investigation team are heading to the scene in the Dadia forest.
The Evros region of north-eastern Greece, not far from the Turkish border, has been ravaged by fires.
A hospital in the city of Alexandroupolis had to be evacuated.
Newborn babies and intensive care patients were among patients moved overnight to a ferry berthed at the port.
An earlier death, also believed to have been a migrant, had been reported in a village close to the coastal city and emergency services had sent mobile text messages to the surrounding areas asking people to leave.
The Dadia national park is a large wooded area to the north of Alexandroupolis, and fires are thought to have spread rapidly there since Monday.
The 18 bodies were found on Tuesday close to the village of Avantas, reports said, when the fire brigade inspected the charred remains of a building.
Fire service spokesman Yiannis Artopios said the possibility was being investigated that the victims had entered Greece illegally, given that there had been no reports of missing residents.
The Evros region has become one of the most popular routes for Syrian and Asian migrants crossing the River Evros from Turkey into the European Union. The Dadia forest is also known to be a route favoured by migrants.
The fire services spokesman stressed that emergency messages had been sent to all mobile phones in the area, including foreign networks.
Fires are raging elsewhere in Greece, whipped up by high winds and temperatures which were set to reach 39C (102F) on Tuesday.
Several villages have been evacuated on the island of Evia and in Boeotia in central Greece. Dozens of nuns were reported trapped when a fire broke out near a monastery to the north-west of Athens.
A fiery, red glow was visible on the fringe of Alexandroupolis in the early hours of Tuesday and satellite images showed several regions of Greece covered in thick smoke.
During the night residents in eight nearby villages were told to leave their homes and head for safety in the city. Later on Tuesday a stream of cars could be seen heading for the city as vegetation along the coast burned.
Flames were seen entering the grounds of the university hospital while the operation was taking place to evacuate the site on the north-east fringe of the city. Greek officials ordered a fleet of ambulances and buses to take some 115 patients away.
While some of the patients were moved to other hospitals in the city, as many as 90 were taken to a ferry, the Adamantios Korais, which has been requisitioned to look after intensive care and new-born babies.
Fires have also been burning dozens of kilometres to the north-west of the city, in Rhodope and further west along the coast in Kavala.
West of the capital, several warehouses became engulfed in flames in an industrial area in Aspropyrgos and close to the Attica Highway the sky darkened with acrid smoke.
Two Albanian workers told the BBC that if helicopters had arrived in time they would have been able to put the fire out.
Around midday on Tuesday a second large fire broke out on the opposite side of the highway in the village of Fyli. Half an hour later residents received a mobile phone message from the 112 emergency number to evacuate the area.
The fire also spread close to the historic Kleiston monastery of the Dormition of the Virgin Mary, a few kilometres north of Fyli in the foothills of Mount Parnitha. Fire service officials say 50 nuns live at the monastery and a disaster response team has been sent to lead them to safety.
Greece is one of several European countries currently at extreme risk of wildfires, according to the EU’s climate monitoring service, Copernicus.
Meanwhile, France endured its hottest ever day on Monday after the mid-August holiday, according to weather service Météo-France.
Temperatures on Monday soared as high as 42.4C in the Drôme area of south-eastern France but the record refers to Monday’s daily average temperature of 26.63C, recorded in 30 weather stations across France.
In Switzerland, the high temperatures have pushed the “zero-degree isotherm” – the height where temperatures fall below freezing point – to a record altitude. MeteoSwiss said the limit had now increased to 5,298m (17,381ft).
The point is shifting steadily higher, mainly because of global warming induced by humans, the Swiss met office says. The increased height of the zero-degree isotherm has been accelerating since the 1970s, especially in spring and summer, it says.