EgyptAir, the national airline of Egypt, said a plane carrying 69 passengers and crew members and flying from Paris to Cairo had gone missing on Thursday, disappearing from radar over the Mediterranean Sea.

“An official source at EgyptAir stated that Flight MS804, which departed Paris at 23:09 (CEST), heading to Cairo has disappeared from radar,” the airline wrote on its official Twitter account.

Later Tweets by EgyptAir said the plane, which was traveling at an altitude of 37,000 feet (11,280 meters), disappeared soon after entering Egyptian airspace.

The aircraft was carrying 59 passengers and 10 crew, while according to flightradar24.com, the plane was an Airbus A320 and its last known position was above the Mediterranean Sea. The airline said among the passengers were 30 Egyptians, 15 French, two Iraqis, and one each from the UK, Belgium, Kuwait, Saudi Arabia, Sudan, Chad, Portugal, Algeria and Canada.

A distress signal was received from EgyptAir flight MS804 by an Egyptian military unit, officials have said.

The Egyptian Civil Aviation Ministry said the unit received the signal from the plane at 4.26am local time (2.26am GMT).

Egyptian aviation officials have said they believe a missing EgyptAir flight has crashed into the sea.

Egyptian armed forces were searching for the plane, whose passengers included one child and two babies. The pilot had 6,000 flight hours, according to AP.

Greece has also joined the search operation for the EgyptAir flight with two C-130 aircrafts, officials at the Hellenic National Defense General Staff said. One frigate is also heading to the area, while helicopters are on standby on the southern island of Karpathos for potential rescue or recovery operations.

CNN aviation correspondent Richard Quest said the plane vanished while cruising the safest part of the journey.

“Planes just do not fall out of the sky for no reason, particularly at 37,000 feet,” he said.

The fact that it entered Egypt airspace and did not report in is highly significant, CNN aviation analyst Mary Schiavo added.

“Since they were 10 miles into Egypt airspace, they should have reported in. If anything had been going on they would have reported at that time,” she said.