Nearly 500 soldiers of the Territorial Defense Force took part in the search near the city of Zamosc in southeastern Poland.
"The Romanian Army's radar surveillance system identified a possible unauthorized breach of national air space, with a signal detected on the route to the town of Galati," the defense ministry said.
To this day, nobody knows why the small jet lost contact minutes after takeoff and crashed down to earth, four and a half hours later.
China has over the past three years regularly flown its air force into the skies near the island, though not into Taiwan's territorial air space.
The Baltic Sea has witnessed in recent months several interceptions by Russian, US and NATO aircraft.
The no-fly announcement rattled regional nerves as it followed shortly after China staged new war games around Taiwan, which Beijing views as sovereign Chinese territory.
The decision could transform Ben Gurion Airport into a global transit hub between Asia and Europe.
An unconfirmed media report said an unidentified object had been spotted in the sky and fighter jets were dispatched to investigate.
That move shortens the distance to Asia by two hours. It makes India, in particular, much more accessible.
“I'll let the intel community and the counterintelligence community figure that out. I haven't ruled out anything,” said General Glen VanHerck.