Aircraft from other EU countries are helping fight the fires

Hundreds of firefighters are tackling fires near the historic city of Coimbra, and other districts remain on high alert.

Water-dropping aircraft provided by other European countries continue to work alongside Portuguese firefighters.

A summer of drought has sparked fires across southern Europe, with Spain and France also fighting flames.

At least 15 people have died and 140,000 hectares have been destroyed in Portugal this year from fires, often started deliberately in bone-dry countryside forests.

Four people, including a former firefighter, were arrested on Tuesday on suspicion of arson, police said. A total of 102 people have been held this year.

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The fire near the university city of Coimbra has been burning since Sunday. More than 400 firefighters are trying to contain the blaze and there are hopes that cooler temperatures could help the situation.

"The intensity of the fire is diminishing considerably, let's see if we are a bit luckier today," the fire chief of nearby Penela, Mario Lourenco, told radio TSF.

Portugal's fire service (SNBPC) said six fires were now under control but three were still burning out of control in the Viseu district.

Duarte Caldeira, of the League of Portuguese Firefighters, said the mainly volunteer firefighting force would suffer exhaustion if the fires continued until the end of the month.

"The firefighting forces are at their limit," he told daily newspaper Correio da Manha. "I have met with firefighters who have been battling blazes since Saturday, with just short breaks of just a few hours to rest."

The European helicopters and planes helping dump water on the fires were sent after an urgent appeal for help by the government.

Disaster fund

A state of emergency has been declared in the Coimbra region, 196km (122 miles) north-east of Lisbon.

Pope Benedict XVI, at his weekly audience in the Vatican, prayed for the victims of the severe weather across Europe, which include fatal floods in Switzerland, Romania and Bulgaria.

The fires have forced villages and homes to be evacuated

"My thoughts go to the regions of Europe hit in recent days by floods and fires which unfortunately have caused victims and great damage," the Pope said.

It was unclear whether Portugal would be eligible for cash payments under the European Union solidarity fund, made available in cases of natural disaster.

The EU suggested Portugal would be eligible, although the country's agriculture minister said the fires had not caused enough damage.

Samuel Infante, of Portuguese environmental group Castelle Branco, told the BBC that poor forest management had contributed to the problem of forest fires.