The fire, which broke out in the afternoon near the village of Kozaki in the Biłgoraj district, had spread across about 100 hectares of forest by nightfall, Polish state news agency PAP reported.
More than 300 firefighters from the Lubelskie and Podkarpackie regions were involved in the operation.
Regional fire chief Zenon Pisiewicz said the situation remained dynamic and could take several more hours to bring under control.
He added that strong air currents were spreading the flames, making firefighting efforts more difficult.
"The fire heats the air, which rises and carries burning fragments of trees, spreading them even hundreds of metres beyond the main fire," Pisiewicz said. He told the media that the blaze was a "crown fire," burning through the tops of mainly coniferous trees, which made it harder to extinguish.
Firefighters were cutting down trees along local roads to create firebreaks, but the flames continued to jump across these barriers, he said.
Water supply has also posed challenges, with crews forced to transport it over long distances or draw it from nearby rivers and reservoirs.
Earlier in the day, one helicopter and three firefighting planes took part in the operation, carrying out a total of five water drops before nightfall.
One of the planes crashed in the area of the firefighting effort, killing the pilot, a spokesperson for the regional governor said.
Authorities said both state-owned and private forests were affected, and the fire posed a threat to a wide area. Forestry personnel from across the region were involved in the response.
Police said a regional road had been closed due to the fire, with traffic diverted to alternative routes.
Emergency services urged the public to stay away from the area and follow official instructions.
(gs)
Source: TVN24, IAR, PAP