ATHENS, Greece — Hundreds of firefighters battled wildfires in Portugal and Greece Sunday, with Spain and Italy sending reinforcements to Portugal to help battle a massive blaze burning for more than three days.

In Greece, authorities on Sunday urged residents of parts of Thessaloniki, the second largest Greek city, to remain indoors and shut their windows and doors due to toxic smoke from a burning recycling plant that was engulfed by a wildfire on the outskirts of the city.

In central Portugal’s Vouzela area, more than 1,200 firefighters backed up by nearly 400 vehicles and 15 aircraft tried to put out a blaze that broke out on Thursday, according to the country’s Civil Protection authority. The wildfire had burned across an area of 12,000 hectares (120 square kilometers, 46 square miles) by Sunday, information from the European Union’s Copernicus satellite mapping agency showed.

The European Union’s Civil Protection and Humanitarian Aid said Spain sent 120 firefighters and 45 vehicles as reinforcements to Portugal on Friday, while three firefighting aircraft from Italy and Spain were also dispatched to help.

On the other side of southern Europe in Greece, a fast-moving blaze at a recycling plant broke out Saturday evening near the Oraiokastro suburb of Thessaloniki, triggering evacuation alerts for three suburbs and a facility housing 157 people with special needs.

Strong winds fanned the flames, and around 160 firefighters were deployed to battle the flames through the night until water-dropping aircraft could take off at dawn, the fire department said.

Oraiokastro mayor Pandelis Tsakiris said on Greece’s state broadcaster ERT that several businesses and homes were damaged by the fire, but that a clearer picture would emerge after authorities conduct a full evaluation.

A 76-year-old man was arrested on suspicion of having started the blaze through negligence by generating sparks with his vehicle that set vegetation near the road alight, the fire department said. He was due to appear before a prosecutor Sunday.

The fire came days after another wildfire in a nearby area killed a 12-year-old boy and his father.

Fire department spokesman Brig. Ioannis Artopoios, speaking on ERT television Sunday, said that about 85% of wildfires in Greece were caused by negligence, including through sparks generated through the use of agriculture machinery, discarded cigarettes and the use of outdoor barbecues. “This means most of them could have been avoided,” he said.

Greece suffers frequent, often devastating, wildfires during its hot, dry summers. In 2018, a blaze east of Athens killed more than 100 people, while a massive fire in 2023 which tore through a remote nature reserve in northeastern Greece was the largest wildfire recorded in the European Union.

The country has increasingly turned to technology to combat the threat of fires, exacerbated by climate change. It is integrating an array of four satellites, launched into low orbit in May, that will monitor for wildfires.

So far this summer, Greece has been spared the heatwaves that have scorched much of western Europe in recent weeks. But it has still seen dozens of blazes across the country, both on the mainland and the country’s islands.