At least 54 people were injured in the blaze Saturday, including eight firefighters and a child. Four of the firefighters were in critical condition Sunday, according to Paulo Santos, an operations and emergencies official with the National Relief Operations Command in Lisbon.
The government has declared three days of mourning.
The head of Portugal’s judiciary police told reporters the fire was started by natural causes.
“We have been able to determine that the origin of the fire was caused by dry thunderstorms,” José Maria Almeida Rodrigues said, according to the Portuguese state-run news agency Lusa.
Some victims were burned to death in their cars as they tried to flee, officials said.