Search and rescue teams are searching near a Greek island for EgyptAir flight MS804 which disappeared en route from Paris to Cairo early Thursday. The flight had 66 people on board.
Egypt and Greece have scrambled search and rescue teams to the southern Mediterranean to search for the plane, as French Prime Minister Manuel Valls said no cause for the disappearance could yet be ruled out.
The Greek army said it had deployed two aircraft, a frigate and two helicopters to the search and rescue operation 130 nautical miles south-southeast of the Greek island of Karpathos. The announcement was in addition to data purportedly showing other marine traffic changing course to help the operation.
Around 11 a.m. London time, Greek authorities said the search was ongoing and that nothing had yet been found.
According to an Associated Press report, citing Egyptian aviation officials, the EgyptAir flight MS804 had crashed in the Mediterranean sea early Thursday morning. There has been no official confirmation and NBC News has not been able to independently verify the report.
Egyptair is updating its Twitter account regularly and said that Egypt's Prime Minister Sherif Ismail had arrived at the airline's crisis center after cutting short a visit to Jeddah.
Asked if he could rule out that terrorists were behind the incident, Prime Minister Ismail told reporters at Cairo airport: "We cannot exclude anything at this time or confirm anything. All the search operations must be concluded so we can know the cause" he said, according to Reuters.
The airline urged restraint from the media in the reporting of the incident amid conflicting reports about distress signals from the missing plane.
Egypt's minister of Civil Aviation is due to give a press conference at 13:30 local time, 12:30 London time (07:30 ET).
News of the incident emerged in the early hours on Thursday. In an Arabic-language Facebook post just before 5 a.m. local time, EgyptAir cited an "official source" as saying the flight, which took off from Paris' Charles de Gaulle Airport at 11.09 p.m. Paris time, had "disappeared from radar in the early hours of (the) day."
In a series of subsequent tweets and statements, EgyptAir said that the plane - an Airbus A320 - was carrying 56 passengers, including one child and two infants, as well as three of the airline's security personnel and seven crew members, taking the total number of people on board to 66.
It also said the plane disappeared 10 miles into Egyptian airspace - a distance confirmed by the country's Civil Aviation Authority, according to Reuters - and that the plane was manufactured in 2003. The "aircraft commander" had 6,275 hours of flight experience, including 2,101 on the same model plane, and the assistant pilot had 2,766 hours of experience, the airline said.
EgyptAir also released a list of the passengers' nationalities: 15 French, 30 Egyptians, two Iraqis and one person each from the U.K., Belgium, Kuwait, Saudi Arabia, Sudan, Chad, Portugal, Algeria and Canada.
French President Francois Hollande spoke to Egpyt's President Abdel Fattah el-Sisi, according to a statement released by Hollande's office in the hours after the disappearance.
"They agreed to cooperate closely to establish as soon as possible the circumstances of the disappearance," the statement said. "The President of the Republic shares the anguish of the families affected by this tragedy."
Reuters reported that Prime Minister Valls told France's RTL radio, "No theory can be ruled out regarding the causes of the disappearance."
The newswire also reported that Greek air traffic controllers had spoken to the plane's pilot while it was flying over Greece and that there was no report of problems.
Ellis Taylor, an Asia Editor at Flight Global magazine, noted the disappearance at 37,000 feet was unusual.
"Accidents are usually at landing or takeoff," he told CNBC. "Something from that height and so far into the flight indicates that something has gone quite seriously wrong on board."
He said that the aircraft type had a good safety record. Shares of Airbus fell 1.2 percent when European markets opened on Thursday, however, and other travel and leisure stocks declined.
Because the flight disappeared in Egyptian airspace, Taylor said he expected search and rescue operations to relatively quickly locate wreckage or an oil slick.