The fire in the area around Viseu, southeast of Porto, started on Wednesday and has grown by 2,000 hectares in the past 24 hours alone. Around 12,000 hectares have now been ravaged by fire.
Nine people have been injured, two of them civilians seriously.
Approximately 1,200 firefighters are trying to control the fire with the help of nearly 400 ground vehicles and 15 aircraft and helicopters.
Spain has sent 120 firefighters and 45 vehicles to Portugal. Three firefighting aircraft from Italy and Spain have also arrived.
A wildfire is also underway outside Greece's second-largest city, Thessaloniki.
Evacuation warnings have been issued for three suburbs, and in parts of the city residents are being urged to stay indoors and keep windows and doors closed due to toxic smoke.
