Southwest flight 1380, a Boeing 737, encountered a problem with the engine shortly after take-off from New York's LaGuardia airport, Robert Sumwalt, chairman of the National Transportation Safety Board, told a news conference.
There was one fatality, he confirmed.
"We are saying this is an engine failure," Sumwalt said, confirming that parts flew out of the engine, which witnesses said hit a jet window, seriously injuring a woman. The identity of the dead person was not immediately disclosed.
"Something is wrong with our plane! It appears we are going down!" wrote passenger Marty Martinez in the caption to a Facebook live-stream video that showed him looking panicked and breathing through oxygen mask.
"Engine exploded in the air and blew open window 3 seats away from me. Explosion critically injured woman sitting in the seat next to the window," he wrote on Facebook.
Flight 1380 landed at Philadelphia International Airport at 11:20 am (1520 GMT) after the crew reported damage to one of the engines, the fuselage and at least one window, the Federal Aviation Administration said.
US television footage showed the jet on the tarmac at Philadelphia surrounded by officials looking at the stricken engine, manufactured by CFM, a joint venture between French company Safran and America's General Electric.
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