A Greek frigate searching for a missing EgyptAir aircraft discovered two large floating objects in a sea area 230 miles south of the island of Crete on Thursday, Greek defence sources said.

The objects appeared to be pieces of plastic in white and red. They were spotted close to an area where a transponder signal was emitted earlier, the sources said. Greek state TV ERT reported similar information, saying two "orange-coloured" objects were located in the same area.

The EgyptAir flight with 66 people on board dropped off radars over the Mediterranean sea about 280 miles off the coast of Egypt. It had been flying from Paris to Cairo.

The airliner made 'sudden swerves' in mid-air and plunged before dropping off radars in the southern Mediterranean, Greek defence minister Panos Kammenos said earlier.

Greek authorities have mounted a search in the area south of the island of Karpathos without result so far, Kammenos said.

"At 3.39 am (0039 GMT) the course of the aircraft was south and south-east of Kassos and Karpathos (islands)," he told a news conference. "Immediately after, it entered Cairo FIR (flight information region) and made swerves and a descent I describe; 90 degrees left and then 360 degrees to the right."

The Airbus plunged from 37,000 feet to 15,000 feet before vanishing from radar, he added.

Officials with the airline and the Egyptian civil aviation department told Reuters earlier they believed the jet had crashed into the Mediterranean between Greece and Egypt. 

Egyptian Prime Minister Sherif Ismail said the search was underway to find the missing Airbus A320 and it was too early to rule out any explanation, including terrorism.

It remained unclear whether the disappearance was due to technical failure or any other reason such as sabotage by ultra-hardline Islamists, who have targeted airports, airliners and tourist sites in Europe, Egypt, Tunisia and other Middle Eastern countries over the past few years.

Egypt Air said the plane sent an emergency signal - possibly from an emergency beacon attached to the plane - at 04:26 am, two hours after it disappeared from radar screens.

In water crashes, an underwater beacon attached to the aircraft's flight recorders starts to emit a signal or ping. This helps search and rescue teams to locate the crash and find the boxes.

The aircraft was carrying 56 passengers - with one child and two infants among them - and 10 crew, EgyptAir said. They included 30 Egyptian and 15 French nationals, along with citizens of 10 other countries.

"The theory that the plane crashed and fell is now confirmed after the preliminary search and after it did not arrive at any of the nearby airports," said a senior aviation source, who declined to be identified.

Asked if he could rule out that terrorists were behind the incident, Prime Minister Ismail said: "We cannot exclude anything at this time or confirm anything. All the search operations must be concluded so we can know the cause."

"Search operations are ongoing at this time for the airplane in the area where it is believed to have lost contact," he told reporters at Cairo airport.

The pilot had clocked up 6,275 hours of flying experience, including 2,101 hours on the A320, while the first officer had 2,766 hours, the airline said.

NO RESPONSE

Greek air traffic controllers spoke to the pilot as the jet flew over the island of Kea, in what was thought to be the last broadcast from the aircraft, and no problems were reported.

But just ahead of the handover to Cairo airspace, calls to the plane went unanswered, before it dropped off radars shortly after exiting Greek airspace, Kostas Litzerakis, the head of Greece's civil aviation department, told Reuters.

"During the transfer procedure to Cairo airspace, about seven miles before the aircraft entered the Cairo airspace, Greek controllers tried to contact the pilot but he was not responding," he said.

Egyptian President Abdel Fattah al-Sisi will chair a national security council meeting on Thursday morning, a statement from his office said. It did not say if the meeting would discuss the plane.

At Cairo airport, authorities ushered families of the passengers and crew into a closed-off waiting area.

EgyptAir said on its Twitter account that Flight MS804 had departed Paris at 23:09 (CEST). It disappeared at 02:30 am at an altitude of 37,000 feet (11,280 metres) in Egyptian air space, about 280 km (165 miles) from the Egyptian coast before it was due to land at 03:15 am..

"There was nothing unusual," EgyptAir vice chairman Ahmed Adel told Reuters. "The search and rescue aircraft from the Egyptian air force are at the position where we lost contact. They are still looking and so far there is nothing found."

In Paris, a police source said investigators were now interviewing officers who were on duty at Roissy airport on Wednesday evening to find out whether they heard or saw anything suspicious. "We are in the early stage here," the source said.

Airbus said the missing A320 had been delivered to EgyptAir in November 2003 and had operated about 48,000 flight hours.

Greece said it had deployed aircraft and a frigate to the area to help with the search. A Greek defence ministry source said authorities were also investigating an account from the captain of a merchant ship who reported a 'flame in the sky' about 130 nautical miles south of the island of Karpathos. - Reuters