Many died while trying to flee the Pedrógão Grande area, 50 km (30 miles) south-east of Coimbra, in their cars, according to the government.
Several firefighters are among the 59 people injured.
“Unfortunately this seems to be the greatest tragedy we have seen in recent years in terms of forest fires,” said Prime Minister Antonio Costa.
The death toll could rise further, he said.
Secretary of State for the Interior Jorge Gomes said that three people died from smoke inhalation and 18...