EgyptAir Flight 804 heading from Paris to Cairo disappeared from radar with 66 people on board over the Mediterranean Sea.
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 for the incident, including terrorism.
Egypt Air said the plane sent an emergency signal - possibly from an emergency beacon attached to the plane - at 04:26 a.m., two hours after it disappeared from radar screens.
In water crashes, an underwater locator beacon attached to the aircraft's flight recorders starts to emit a signal or ping. This helps the search and rescue teams to locate the boxes, and the location of the crash.
The aircraft was carrying 56 passengers, including one child and two infants, and 10 crew, EgyptAir said. They included 30 Egyptian and 15 French nationals, along with nationals from 10 other countries.
Source: CNN, Reuters