What we know: 150 people were on board
What caused the crash?
The cause of the crash has not yet been determined, the Germanwings CEO said.
Lufthansa, which owns Germanwings, called the crash "an accident."
"For the time being we are calling this an accident," a Lufthansa official said at a news conference in Barcelona today. "Everything else is speculation."
The French Interior Ministry said the plane's black box has been found and that it will be analyzed in the coming hours.
The plane was flying at 38,000 feet -- its normal cruising altitude -- when it started to lose altitude and descended for 8 minutes, according to Germanwings. When the plane was at 6,000 feet, it lost contact with French radar.
Earlier in the day, the plane flew from Dusseldorf to Barcelona, where it arrived on time, according to Germanwings. The plane had been checked on March 23 in Dusseldorf.
The airline said the plane went into operation in 1990. It was sold to Lufthansa in 1991 and then sold to Germanwings in 2014. The plane had 58,313 flight hours, the company said.
Who was on board?
The passengers were German, Spanish and Turkish, said Spanish King Felipe IV, who was in France for a pre-scheduled meeting with Hollande. The King had planned to stay in France for three days but now said he is returning to Madrid to launch a crisis center.
Germanwings said it is believed 67 Germans were on board.
Sixteen students and two teachers from a school in Haltern, Germany, were on the flight, a spokesperson for the city of Haltern said. The students had been returning from an exchange trip in Barcelona.
Opera singers Oleg Bryjak and Maria Radner were also among the passengers, returning from a performance in Barcelona. Radner was on the flight with her husband and baby.
The State Department is reviewing whether any Americans were on board.
The list of nationalities of the casualties will be released as soon as the airline is certain, Winkelmann said, adding that the victims' families will be informed before a list of names will be released.
At a White House press conference, President Obama offered his thoughts and prayers to the people of Germany and Spain, saying "American stands with them at this moment of sorrow."
Obama said he has called German Chancellor Angela Merkel and hopes to speak with Prime Minister Mariano Rajoy of Spain to "express the condolences of the American people" and to offer U.S. assistance as they investigate this "awful tragedy."
"Our teams are in close contact and we're working to confirm how many Americans may have been on board," Obama said.
Could there be a terror link?
ABC News' Molly Hunter contributed to this report.