The country's defence forces were put on high alert after an unauthorised aircraft entered Bulgarian airspace.
ADVERTISEMENTBulgarian authorities are searching for a mysterious pilot who flew unauthorised across several European countries.
Defence forces in the country were placed on high alert on Wednesday evening when a small aircraft was detected in its airspace.
The two-seater Beechcraft plane had apparently departed from Hungary and flown over Poland and Slovakia, according to Interior Minister Boiko Rashkov.
The pilot is then believed to have landed near the Black Sea, after briefly crossing into Serbia and Romania.
The 60-year-old aircraft was finally found on the runway of a private airport in the northeast area of Buhovtsi. It was covered by a tarpaulin and there was no trace of the crew.
The suspicious aircraft had no flight plan, had deactivated its transponders and did not respond to radio messages or visual signals, Bulgaria's defence ministry said in a statement.
The Beechcraft plane was intercepted by four Hungarian and Romanian fighter jets then escorted until it entered Bulgarian airspace.
Bulgarian defence minister Dragomir Zakov told reporters that Bulgaria didn't send up fighter jets to intercept as the aircraft "did not represent a threat at any time."
"It was flying at a very low altitude and with low speed, which makes interception by fighters difficult," he added.
According to the Defence Ministry, weather conditions were also difficult with heavy rains and thunderstorms. The plane reportedly stopped in the town of Vidin in northwest Bulgaria to refuel. From there it travelled east to an abandoned airfield near Targovishte.
Here authorities discovered it with the engine still warm, Interior Minister Boyko Rashkov told journalists. The pilot, however, had completely vanished without a trace.
The prosecutor's office in Varna, eastern Bulgaria has opened an investigation into the incident.