The first victim, a man in his 60s, burned to death as he helped firefighters battle the fire which broke out Sunday afternoon in a mountainous region near Silvares, 260 kilometres (160 miles) north of Lisbon.

A second man was later found burned to death in his car near Povoa da Ribeirinha in the same area.

More than 500 firefighters and 600 soldiers were battling against steep terrain, strong easterly winds and temperatures which soar to nearly 40 degrees Celsius (104 degrees Fahrenheit) during the day.

The firefighters, who have come from all over the country, are equipped with 145 vehicles, four helicopters and six fire-fighting planes, including two on loan from neighbouring Spain.

Officials said they could not predict when the fast-moving fire, which is burning along three fronts and has already destroyed more than 4,000 hectares (10,000 acres) of pine trees, would be brought under control.

Interior Minister Antonio Figueiredo Lopes said the thickness of the brush was preventing firefighters from reaching many areas which are burning while the extreme heat was rendering water-dropping aircraft useless.

"Given the high temperatures and the dryness of the terrain, the water pratically evaporates when it touches the ground," he said.

"Unfortunately the fire broke out in an area where it is very difficult to fight it and the presence of firefighters is almost impossible," he added.

The minister said the government would bring in more bulldozers so that paths could be cleared in the forest to allow firefighters to reach the flames.

The weather office forecast the high temperatures would continue until at least Sunday.

Four villages were surrounded by fire but firefighters said there was no risk to homes as the flames were at least 600 metres (yards) away.

But despite the assurances from firefighters, many area residents were using buckets and garden hoses to help put out the flames in an effort to make sure the fire did not reach their properties.

"All we can think about now is protecting our homes," resident Joao Cacoila told state television RTP.

Officials said there were signs that the fire had been started deliberately.

Forests cover roughly one-third of Portugal and forestry accounts for 11 percent of the nation's exports, but each summer thousands of trees are destroyed by fires.

There were some 25,000 forest or brush fires last year in Portugal which burned almost 120,000 hectares (296,400 acres) of land, according to forest service figures.

Officials blame a large number of the fires on arsonists. Of the 164 largest fires which flared last year, firefighters believe 30 percent were started on purpose.

Environmentalists argue a large number of fires could be avoided if the government did more to clear forests of overgrown areas, which can easily ignite during the dry summer months, and cracked down harder on arsonists.

Of the 185 trials for arson held between 1997 and 2002, only four resulted in jail sentences.

TERRA.WIRE