LISBON, Portugal (AP) -- Forest fires flared up again Wednesday in central Portugal _ just hours after firefighters brought the flames under control after fighting a dozen blazes for four days.
More than 540 firefighters supported by 150 fire trucks and seven air tankers were fighting blazes in the Coimbra district alone. Firefighters also were battling forest fires in the central and northern districts of Porto, Santarem, Vila Real, Viseu.
Four more people were arrested Wednesday on suspicion of arson - raising to 122 the number of people arrested in 2005 on suspicion of deliberately starting forest fires.
Portugal has had little or no rain for 10 months, with at least 75 percent of the country in the midst of an extreme drought, the Water Institute said.
After days of fires, a cooling fog and higher humidity helped firefighters bring the flames under control Wednesday before they flared up again, officials said.
The fire has destroyed at least 10 houses in the suburbs of the city of Coimbra, about 200 kilometers (120 miles) north of Lisbon. About 50 residents were evacuated from villages Tuesday night, officials said.
Some residents were due to return to their homes, Coimbra's Gov. Henrique Fernandes said Wednesday. Many will return to a blackened landscape, with only charred soil where trees and crops once stood.
In total, more than 1,620 firefighters were fighting fires, and about 600 members of the armed forces were deployed to areas where fires were under control.
Several countries, including Spain, Germany, France and the Netherlands, sent pilots and equipment. Slovakia also said it was prepared to send a helicopter.
In the Miranda do Corvo area of Coimbra, residents applauded as German helicopters helping to fight the blaze flew overhead, dousing flames with water, the Jornal de Noticias newspaper said.
''As soon as they got here, they rolled up their sleeves and set up a communications room,'' Portuguese Air Force pilot Mario Marcao told the newspaper.
Three French firefighters from a special natural disasters unit in Nice, France, cut short their vacations to help out, flying to Portugal driving straight to the north.
Women walked long distances to bring drinking water, wine, juice and food to firefighters working days on end. Other residents helped by bringing crews buckets filled with water.
President Jorge Sampaio thanked the firefighters, and renewed an appeal Wednesday to employers that have workers trained as firefighters to release them to fight the blazes.
''We must improve management of Portugal's forests,'' he said. ''From September, all our energies must be focused on this.''
The fires have not spread to the Algarve, the country's primary tourist destination, but officials warned that the region's water supply could be threatened next year unless if it doesn't receive abundant rain over the winter.
So far this year, wildfires have killed 15 people, 11 of them firefighters. Fires have burned through 180,000 hectares (445,000 acres) so far, compared to the total area burned last year, 129,652 hectares (320,370 acres).
A firefighting plane crashed Wednesday in Valadares in the district of Viseu, slightly injuring a Spanish pilot, officials said.
Other parts of southern Europe also faces fires. In Spain, enduring its driest year since keeping rainfall records in the 1940s, dozens of fires were burning in the northwest Galicia region and other areas.
In Italy, a fire in Sicily burned 100 hectares (247 acres) of forest and about 10 hectares (25 acres) burned Tuesday in Puglia, Italian officials said.