Five thousand firefighters are struggling to contain multiple wildfires raging across northern Portugal that are blamed for causing at least six deaths and forcing an unknown number of residents to flee their homes.

More than 5,000 firefighters have been tackling the wildfires that Portuguese Prime Minister Luís Montenegro said are "raging across the country".

Three firefighters died battling the blazes, Portugal’s prime minister said, adding the country was going through “difficult days.”