SOFIA (REUTERS) - A bomb threat that turned out to be a hoax forced a passenger plane en route from Warsaw to Egypt to make an emergency landing in Bulgaria on Thursday (Nov 19), the operator of the aircraft said.

The Airbus A320 landed just before dawn in the Black Sea city of Burgas, where the authorities said all 161 passengers and crew were evacuated safely.

"A passenger informed the cabin crew about the explosive he might be carrying," Small Planet Airlines, which operated the flight, said in a statement.

"(He) ... later admitted it was a joke."

Police were questioning the man, a 67-year-old Polish citizen, the carrier said.

Bulgarian special forces had found no explosives in an initial sweep of the plane and were conducting a second check, a police spokesman said, without confirming the threat had been a hoax.

She said a passenger who alerted crew about a possible bomb on board later admitted having consumed alcohol. The plane was en route to the Red Sea resort of Hurghada.

Small Planet Airlines said it was sending another aircraft to Burgas airport to enable the passengers to complete their journey.

The spokesman said the airport remained closed.

"The plane landed in Burgas at 5.48 am (11.48am Singapore time) after a request for flight number LLP8015 travelling from Warsaw to Hurghada to make an emergency landing, due to a report of the presence of explosives on board," the press officer said.

A passenger who alerted crew about a possible bomb admitted on questioning to having consumed alcohol, a police spokesman said.

A passenger identified as Agata Pinuszewska told Polish broadcaster TVN24 that the plane diverted to Burgas after another passenger shouted that he had a bomb.

"After landing the plane stayed about an hour (on the tarmac)... Anti-terrorist police entered the plane and started to shout to this man 'where do you have this bomb?'. Then we were walked out of the plane," she said.

A spokesman for Polish national carrier LOT said the aircraft did not belong to the airline but was a charter, destined for the Egyptian city of Hurghada.

It was towed to a remote location at Burgas airport, where it was undergoing a second check by Bulgarian special forces, a police spokeswoman said.

Bulgaria had tightened controls at its borders and airports in recent days, she added, following Friday's militant attacks in Paris in which 129 people died.

Mr Jakub Flasinski, vice-consul at the Polish embassy in Sofia embassy, said the authorities were awaiting final confirmation that the plane was safe.

The airline would decide whether the flight continued its route or headed back to Warsaw, the Burgas mayor told reporters.