LISBON (Reuters) - Fires in Portugal have burnt 240,000 hectares (600,000 acres) of forest this year, Interior Minister Antonio Costa was quoted as saying.

The fires, sparked by the worst drought in the country's history, have decimated forests in central and northern Portugal, damaged the paper industry, killed 14 people and prompted the evacuation of villages since they began in May.

The government's last official estimate made in mid-August was 134,500 hectares destroyed and the fires are now rated the second most destructive since 1980, news agency Lusa quoted Costa as saying late on Tuesday.

Paper company Portucel, Portugal's biggest owner of forests, says it has suffered serious losses but has given no details. The pulp and paper sector makes up about 10 percent of Portugal's exports.

Costa said that if fires persist the government would extend beyond September 30 its official high-risk fire season to let it maintain volunteer fire fighters in action.

Aircraft from Italy, France, Germany, Spain and the Netherlands have helped Portugal fight the fires. Portugal's worst burning season since 1980 was in 2003, when 425,000 hectares of forest burnt.