Thousands of residents fled to safety from a wildfire that burned for a fourth day north of Athens early Friday, during an overnight battle to stop the flames reaching populated areas, electricity installations and historic sites.

In heat wave conditions, the blaze tore through forest areas 20 kilometers (12.5 miles) north of the capital, destroying more homes. Ground crews of several hundred firefighters dug fire breaks and hosed the flames.

Traffic was halted on the country’s main highway connecting Athens to northern Greece, as crews tried to use the road as a barrier to stop the flames advancing before water-dropping planes could resume at first light. But sparks and burning pine cones carried the fire across the highway at several points.

Several firefighters and volunteers were hospitalized with burns, health officials said.