MADRID (AP) — Hundreds of firefighters are struggling to contain a wildfire in northeastern Spain that has spread over 5,500 hectares (13,590 acres) and forced the evacuation of 53 residents.

A Spanish military unit with 120 specialists has joined local firefighters, who had worked overnight to control the blaze that is raging in difficult hilly terrain near the Ebro River.

Miquel Buch, the regional interior minister, said Thursday 20,000 hectares are under threat in what is the worst fire in the Catalonia region in two decades.

Buch says authorities suspect the cause of the outbreak was a deposit of improperly stored manure.

Firefighters say that high temperatures and a drop in humidity will likely fan the flames.