Poland says it has detected what appears to be an observation balloon in its airspace that flew in from the direction of Belarus.
The country's defence ministry tweeted that radar contact with the object was lost near Rypin, a town in central Poland around 180 miles from the border with Belarus.
The object was spotted Friday around 8.30pm and radar monitoring was carried out, but the object ceased to be visible at around 12.30am on Saturday, the armed forces said.
It is an incident that is likely to conjure memories of the Chinese spy balloon which passed over the US, causing a diplomatic row and concerns over national security.
The development follows two other known incursions into Poland's airspace since Russia launched its full-scale invasion of Ukraine, which lies on Poland's eastern border.
In November, two Polish men were killed when a missile landed in eastern Poland.
Western officials said they believed a Ukrainian air defence missile went astray as Ukrainian air forces tried to repel a large-scale attack by Russia.
Polish military and political officials are also facing questions about another object that landed on Polish territory in December, but which was only discovered in April by chance by a member of the public who was riding a horse in a forest.
The issue is raising questions about the authorities' handling of its air defences amid new risks created by the war in Ukraine.