At the airport in Nairobi, worried families gathered.
"I came to the airport to receive my brother but I have been told there is a problem," Agnes Muilu said. "I just pray that he is safe or he was not on it."
Kenya's transport minister, James Macharia, said that authorities had not yet received the passenger manifest. He said an emergency response had been set up for family and friends.
"My prayers go to all the families and associates of those on board," Kenya's President Uhuru Kenyatta said.
In a statement, Boeing said it was "deeply saddened" to hear of the crash and that a technical team was ready to provide assistance at the request of the US National Transportation Safety Board.
In October, another Boeing 737-8 MAX plunged into the Java Sea just minutes after taking off from Jakarta, Indonesia's capital, killing all 189 people on board the Lion Air flight. The cockpit data recorder showed that the jet's airspeed indicator had malfunctioned on its last four flights, though Lion Air initially claimed that problems with the aircraft had been fixed.
AP and AFP contributed to this story.
Lucie Morangi and Liu Hongjie reported from Nairobi, Kenya.
