Police said a German tourist had drowned while trying to escape by boat from a fire-stricken area on the Halkidiki peninsula in the country’s northeast.
The fire burned out of control on two main fronts, about 80 kilometres south of Thessaloniki, Greece's second largest city.
Several thousand people fled the blaze, which destroyed or seriously damaged more than 50 homes and dozens of cars.
Earlier, coast guard and private boats picked up stranded tourists and local residents from beaches in the Cassandra area.
Fire officials said there had been indications of arson.
"This is a major fire, and a disaster has been declared in the area. With the daylight, firefighting planes are being used and that is helping this effort," said Giorgos Kalatzis, minister for Greece's Macedonia and Thrace administrative regions.
Ten water-bombing planes and helicopters began assisting the effort at first light, as more than 250 firefighters and soldiers battled the fire that swept over rugged terrain, fanned by gusts of wind and temperatures reaching 40 degrees Celsius.
Mr Kalatzis said he hoped the fire could be contained by later on Tuesday.
At least 50 people -- mostly Greeks -- were hospitalised with breathing problems and several people were being treated for burns.
The fire broke out amid a heat wave across southeast Europe, with temperatures in some areas reaching 42 degrees Celsius.