CAIRO, Egypt -- EgyptAir Flight 804 vanished from radar on its way from Paris to Cairo with 66 people aboard, the airline said Thursday.
The plane was flying at 37,000 feet when it lost contact overnight above the Mediterranean Sea, the airline tweeted.
Somber relatives gathered in Cairo and Paris airports, seeking word on their loved ones. They were ferried to special centers at both airports, where translators and psychiatric support awaited.
What we know so far:
-- Passengers on board the Airbus A320 included three children -- two of them infants, said Capt. Ahmed Adel, a vice chairman at EgyptAir.
-- The flight left Charles de Gaulle Airport at 11:09 p.m. Wednesday local time and was supposed to land in Cairo at 3:15 a.m. Thursday. Both the departure and arrival cities are in the same time zone.
-- The location of last contact was 173 miles (280 kilometers) from the Egyptian coast, the airline tweeted.
-- There was no special cargo on the flight and no notification of any dangerous goods aboard, Adel said.
-- Before Paris, the jet also made stops in Eritrea and Tunis, data from flight tracking websites show.
-- The plane has been part of EgyptAir's service since November 3, 2003, he added. It had about 48,000 flight hours.
-- The plane's captain had about 6,000 flying hours, Adel said.
-- The plane had routine maintenance checks Wednesday in Cairo, before it left for Paris, an airline official said.
-- A distress signal was detected at 4:26 a.m. -- about 2 hours after the jet vanished -- in the general vicinity where it disappeared, Adel said.
-- He said the distress signal could have come from another vessel in the Mediterranean. Egyptian armed forces stressed that they had not received a distress call.
-- There's no confirmed information on the status of the missing plane, Egyptian Prime Minister Sherif Ismail said. Egypt's President Abdel Fattah el-Sisi has convened a meeting with security officials.
-- The Egyptian navy is conducting search and rescue operations with help from Greece.
-- Greek air traffic controllers spoke to the pilot at 2:27 a.m. Cairo time, but the pilot did not mention any problems, aviation officials said.
-- The plane left Greek airspace a minute later and entered Egypt's airspace. Two minutes later, Greek radars lost touch with it.
-- Greece is taking part in the rescue operation 130 nautical miles southeast of Karpathos island. Greece said its armed forces deployed a military aircraft and a helicopter.
Nationalities of those aboard
Passengers and crew were from France, Egypt, Britain, Belgium, Iraq, Kuwait, Saudi Arabia, Sudan, Chad, Portugal, Algeria and Canada.
A majority were French and Egyptian -- 15 and 30 people respectively, the airline said in a statement.
In Cairo's airport, dozens of relatives paced anxiously in a building set aside for families. Others shouted at photographers taking pictures of them while some berated officials over the perceived lack of information.
The rest of the airport hummed with life, like any other day, CNN's Ian Lee reported.
Analysts weigh in
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.
Experts said while it's too early to determine what happened, the first priority is to find survivors.
"Find the plane, find the people, see if there are folks that could be rescued," said David Soucie, a CNN aviation safety analyst.
"Safety people are looking at safety issues, maintenance people looking at maintenance issues, security people looking at security issues."
Conditions were clear and calm when the plane crossed over the Mediterranean Sea, according to CNN meteorologist Pedram Javaheri.
"The area in question in the eastern Mediterranean is currently under clear skies, but computer models suggest a storm system may impact the region as early as Friday afternoon," he said.
"Once the plane reached the Adriatic Sea, several hours into its journey, clouds were beginning to clear and it remained that way for at least another 1-2 hours before the plane's final known location."
If there are any survivors, there's still a window to save them.
"The water temperatures in the eastern Mediterranean near Egypt are in the low 20s Celsius [mid to low 70s Fahrenheit]," Javaheri said.
"Survival times in such waters range from 2-7 hours for the elderly or individuals in poor health, while they range anywhere from 2 to 40 hours for healthier individuals."
Egypt's aviation incidents
Egypt is no stranger to aviation disasters.
In March, an "unstable" man diverted an EgyptAir flight from Alexandria to Cyprus. The suspected hijacker later released all hostages and surrendered.
Last year, a Russian plane exploded midair over the Sinai Peninsula, killing all 224 people aboard. Egyptian officials initially downplayed Islamic militants' claim that they brought down the jet, saying technical failure caused the crash.
And in 1999, an EgyptAir passenger jet made a rapid descent, plunging almost 14,000 feet in 36 seconds.
The Boeing 767, en route to Cairo from New York City, crashed into the Atlantic Ocean off the Massachusetts coast in October of that year.
Though its debris was later found, speculation remains on the cause of the crash that killed all 217 people on board.
CNN's Euan McKirdy, Nic Robertson, Isaac Linsay Schams Elwazer, Chris Liakos, Elaine Ly and journalist Sarah Sirgany contributed to this report