It was the latest in a series of airspace incursions in countries on NATO's eastern flank, including Romania and the Baltic states, that have fuelled fears of the war in Ukraine spilling over the alliance's borders.
Poland scrambled fighter jets to secure its airspace after Russian air strikes killed at least eight people in neighbouring Ukraine, in attacks that extended as far as the western city of Lviv.
Tusk told an emergency meeting that everything suggested the object was a Russian Kh-101 missile but Polish officials wanted to be 100 per cent certain about the type of missile and who launched it.
"There was no direct threat because the missile landed in an uninhabited area; we were ready to shoot it down had it continued its flight," he added.
The Kh-101, an air-launched cruise missile that can fly more than 2500km according to military experts, has been a workhorse of Russian missile strikes on Ukraine since the full-scale invasion in 2022.
Tusk later visited the site where the object fell, near the village of Tarnawa-Kolonia, about 100km from the Ukrainian border.
"There is no reason to think the target was Poland," he said, adding that Ukrainian fighter pilots had attempted to shoot down missiles approaching the Polish border.
Tusk vowed to maintain support for Ukraine, saying his government would consider providing further aid including additional Patriot systems.
Bilateral relations have recently been strained by disputes over history.
Ukraine's Foreign Minister Andrii Sybiha said earlier in a post on X that a Russian Kh-101 cruise missile crossed into Poland.
The Russian embassy in Warsaw did not immediately respond to an emailed request for comment.
NATO Secretary General Mark Rutte said he had discussed the situation with Tusk.
"This incident is yet another reckless act by Russia and a dangerous consequence of its war against Ukraine," Rutte wrote on X.
The object left a crater about 10 metres wide, the Polish interior ministry added on X.
According to local authorities, it was located in farmland about 2km from residential buildings.
Local resident Roman Bartoszek, who lives about 4km from where the object fell, said he had heard aircraft overhead and his windows had shaken.
The operational command of Poland's armed forces said an object had been detected in Polish airspace at 3.40am on Thursday and disappeared from radars soon afterwards.
An Mi-24 helicopter later went to the crash site.
Police had received reports of a large bang and went to the site where they found the crater.
ukr
