"Polish and allied aircraft are operating in our airspace, while ground-based air defence and radar reconnaissance systems have been brought to the highest state of readiness," Poland's operational command said in a post on X.
Eastern-flank NATO members are on high alert after Poland shot down suspected Russian drones in its airspace in September and drone sightings and air incursions, including in Copenhagen and Munich, have led to chaos in European aviation.
Lithuania's airport in Vilnius was closed for several hours overnight after reports of a possible series of balloons heading towards the airport late on Saturday.
All of Ukraine was under air raid alerts for several hours overnight, with Ukraine's air force issuing warnings of missile and drone attacks for the Lviv region.
The region's governor later confirmed two people had been killed with another two injured.
Andriy Sadovyi, the mayor of Lviv - about 70 kms from the border with Poland - said the city's air defence systems were engaged heavily in repelling first a drone and then a Russian missile attack.
Parts of the city were left without power and public transport was yet to start running, with Sadovyi saying on the Telegram messaging app that it was "dangerous to go out into the streets."
Witnesses said the pounding of what sounded like air defence systems in operation came from all directions.
A late Saturday night attack on the city of Zaporizhzhia left one person dead and nine injured, Ivan Fedorov, the regional governor said on Telegram.
"Apartment blocks and private houses were damaged, cars burned," Fedorov said. "Windows were blown out, yards wrecked."
More than 73,000 customers in the southeastern region were left without power, he added.
There has been no immediate comment from Russia about the Saturday overnight attacks.
Both sides have been launching air attacks throughout the war aimed at destroying infrastructure deemed crucial to the overall war efforts, including energy and transport facilities.
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