About half an hour before Emirates Airline Flight 203 landed in New York on Wednesday, a crew member told passengers they would not immediately disembark because of ill people on board.
But a passenger from New York, Erin Sykes, said the problems began even before the plane was airborne.
“It was clear people were sick before they even got on the plane, so much so that I asked the stewardess for a mask,” she said. “People were coughing the whole flight, like phlegmy, really gross coughs.”
The authorities, including the Centers for Disease Control and Prevention, are working to determine what made about 100 passengers feel sick on the flight that landed at Kennedy International Airport from Dubai, United Arab Emirates, at about 9:20 a.m.
The pilot alerted officials on the ground after dozens of passengers reported feeling ill, said a law enforcement official who spoke on condition of anonymity because he was not authorized to speak about the incident.
Eric Phillips, a spokesman for Mayor Bill de Blasio, wrote on Twitter at about 12:30 p.m. that 19 people were sick. Ten were taken to Jamaica Hospital Medical Center, and nine refused medical attention, he said. There were 521 people on the plane.
A spokesman for the hospital said passengers had coughs, headaches, sore throats and fevers.
The rapper Vanilla Ice, whose given name is Robert Van Winkle, wrote on Twitter that he was on the plane but unaware of the illnesses before landing.
At the airport, Musaab Mohamed, 38, of Hamden, Conn., arrived just before 11 a.m. to pick up his wife and three daughters — ages 7, 5 and 1 — who were returning home from a trip to Sudan. He heard from another person who was waiting for a passenger that the flight was on lockdown.
“They said it was a virus,” Mr. Mohamed said.
He spent the next half-hour being shuttled from desk to desk inside the sprawling terminal, upstairs and downstairs, trying to learn more, he said.
“I cannot even contact my wife,” Mr. Mohamed said after repeatedly calling her cellphone. “Nobody is giving me any information.”
Passengers began trickling out of Terminal 4 around noon, many talking about the long wait to disembark after a 14-hour flight.
“We saw medical teams, police, everything — everybody like waiting for the plane,” said Ishtiaq Khan, 19, of the Bronx, who was returning with his mother from a trip to Bangladesh.
“My dad called me, like, 30 times.”
Mariana Alfaro, J. David Goodman, Sean Piccoli and Ali Winston contributed reporting.
