Romania also scrambled fighter jets on Saturday when a drone breached the country's airspace during a Russian attack on Ukrainian infrastructure near the border, the defence ministry said.
The incidents came after multiple Russian drones crossed into Poland on Wednesday, prompting NATO to send fighter jets to shoot them down.
The Polish military's operational command posted on X on Saturday afternoon that ground-based air defence and reconnaissance systems were on high alert.
The alert lasted around two hours.
It stressed that "these actions are preventive in nature," and were aimed at securing Poland's airspace and protecting the country's citizens.
It cited a threat of drone strikes in regions of Ukraine bordering Poland, but didn't immediately give further details.
Prime Minister Donald Tusk also posted that "preventive air operations" had begun in Polish airspace because of the threat posed by Russian drones operating over nearby areas of Ukraine.
The Polish Air Navigation Services Agency said that Lublin Airport was closed to air traffic "due to military aviation activities".
It didn't specify how long that would last, but airport spokesman Piotr Jankowski told the PAP news agency that the airspace above the airport was closed until the early evening.
Later Saturday, the military's operational command wrote on X that the operation "has been completed" and that ground-based defence and reconnaissance systems had returned to normal.
Romania, a European Union and NATO state which shares a 650-km (400-mile) border with Ukraine, has had Russian drone fragments fall onto its territory repeatedly since Russia began waging war on its neighbour.
On Saturday, Romania scrambled two F-16 fighter jets and warned citizens in the southeastern county of Tulcea near the Danube and its Ukrainian border to take cover, the defence ministry said in a statement.
It added that the jets detected a drone in national airspace, which they followed until it dropped off the radar 20 km southwest of the village of Chilia Veche.
"The drone did not fly over inhabited areas and did not pose an immediate danger to the population," the statement said.
Russia has said it didn't target Poland on Wednesday, and Moscow's ally, Belarus, said that the drones went astray because they were jammed.
But European leaders have expressed certainty that the incursions were a deliberate provocation by Russia.
US Secretary of State Marco Rubio on Saturday said the incursion of Russian drones into Polish airspace this week was unacceptable, but that it remained unclear if Russia had deliberately sent the drones intoPolish territory.
with Reuters
