Poland's defence ministry said on Twitter on Saturday that an unidentified object had entered the country's airspace from Belarus and may be a surveillance balloon.
The country's flight control center spotted the object before it disappeared from radar screens near the city of Rypin, deep in Poland's interior.
NATO member Poland is on alert for any breaches of its airspace as war rages in neighbouring Ukraine and after rocket landings in November and December.
The ministry said radar communication was cut near the town of Rypen in north-central Poland. A spokesman for Poland's regional defence force said the body was being searched. Authorities in Russia or Belarus could not be reached for comment.
After two Poles were killed in November by what Warsaw concluded was a Ukrainian air defence missile that missed the target, and the discovery of a military object in northern Poland in April, national security has become a key issue in Poland ahead of elections later in the year.
Poland's defence minister, Mariusz Blaszczyk, recently faced criticism after debris of what might be a rocket was found in the woods near Zamość, a small town outside the Polish city of Bydgoszcz.
The Defense Ministry later admitted that the wreckage "may have been a missile" that entered Polish airspace on Dec. 16, but the airspace control center did not immediately alert the ministry.