High temperatures and dry weather are hampering efforts to extinguish a host of wildfires across Portugal.
Portugal said it could not cope alone in tackling the fires
Some blazes have been brought under control, but a string of villages and the ancient city of Coimbra remain threatened by about a dozen fires.
Villagers returning to their homes have described how fires tore through some 140,000 hectares and destroyed homes.
A summer of drought has sparked fires across southern Europe, with Spain and France also fighting flames.
At least 15 people have died in Portugal this year from fires, often started deliberately in bone-dry countryside forests.
Four people, including one former firefighter, were arrested on Tuesday on suspicion of arson, police said. A total of 102 people have been held this year.
Central and northern Portugal have been hit the worst, and fires are still threatening the outskirts of the third-largest city of Coimbra.
More than 300 firefighters were working to contain flames on the edge of Coimbra, which has a population of 100,000.
Fire-fighting aircraft from several EU states joined some 3,000 Portuguese firefighters following an urgent appeal for help by the government in Lisbon.
Hopes were raised on Tuesday when winds and temperatures dropped and humidity levels fell, before the afternoon sun re-emerged.
The burnt body of an elderly woman was discovered by firefighters but it was not clear if she was killed by the flames.
Other villagers described the destruction wrought by the flames.
"It's a catastrophe. People lost everything. I just turned 80, and I can say these are worst fires I have seen," Maria Carvalho da Silva told the AFP news agency.
"We always had forest fires, but I don't know why they were easier to put out."
The BBC's Paul Henley, reporting from the town of Abrantes some 80km (50 miles) north of Lisbon, says the damage is plain to see.
Our correspondent describes a wall of thick fog across a parched hillside and a darker, grey-black smoke gathering at ground level.
The fire has managed to cross a four-lane motorway without pause, he adds, charring trees, burning grass and tearing roofs from farm buildings.
The fast-moving wildfires have already destroyed at least 12 houses in the suburbs of the Coimbra, 196km (122 miles) north-east of the capital, Lisbon.
A state of emergency was declared in the region.
It was unclear whether Portugal would be eligible for cash payments under the European Union solidarity fund, made available in cases of natural disaster.
Smoke from the fires is visible from space. (Pic: ESA)
The EU suggested Portugal would be eligible, although the country's agriculture minister said the fires had not caused enough damage.
Firefighting aircraft from France, Spain, Germany, the Netherlands, and Italy, joined the efforts against the fires on Tuesday, answering a call to help from Portugal, which does not maintain a fleet of water-carrying planes.
Samuel Infante, of Portuguese environmental group Castelle Branco, told the BBC that poor forest management had contributed to the problem.
Planting different types of tree would help prevent fires, he said, but private ownership of forests restricts co-ordinated action, he said.