A forest fire in the Pedrógão Grande area in central Portugal has killed at least 61 people and injured at least 54, according to the Associated Press.

The fire began on June 17 and later engulfed parts of two adjacent cities, Castanheira de Pera and Figueiró dos Vinhos. The Portuguese government has established a national period of mourning from Sunday to Tuesday in honor of the victims of the fire, which continues to burn as 1,600 firefighters along with police and military personnel work to stop it.

Portuguese Prime Minister António Costa said Sunday that more deaths could be confirmed as efforts to recover bodies continue, and that “the dimension of this fire has caused a human tragedy beyond any in our memory.” Victims are still being identified.

Many victims died inside their vehicles as they drove on nearby roads in attempts to avoid the blaze, CNN reported.

Portugal’s National Civil Protection Authority warned that high temperatures and potentially strong winds could aggravate the fire. Some officials have suggested that dry thunderstorms caused the flames, The New York Times reported.

In a statement, the European Commission said they could provide aircraft, while Spain and France also offered aircraft. The Portuguese government will also establish four emergency support centers in affected and surrounding areas, according to a statement on its website.