Greek authorities told parts of Thessaloniki to stay indoors and seal windows and doors after wildfire smoke turned toxic when flames engulfed a recycling plant near Oraiokastro.
A 76-year-old man was arrested on suspicion of starting the blaze through negligence after sparks from his vehicle allegedly ignited roadside vegetation; he was due before a prosecutor Sunday.
About 160 firefighters battled the fire overnight, while the blaze had already triggered evacuation alerts for three suburbs and a facility housing 157 people with disabilities; businesses and some homes were damaged.
Elsewhere in Greece, 210 firefighters and 29 aircraft were deployed against a new wildfire west of Athens, as officials said roughly 85% of the country's wildfires are caused by negligence.
Across southern Europe, Portugal's biggest blaze had burned 12,000 hectares and Spain's Girona fire nearly 2,200, underscoring a wider regional wildfire strain intensified by hot, dry conditions.