An Emirates flight from Dubai has landed in New York with numerous sick passengers on board, NBC New York reports. The passengers got sick overnight, but it’s not clear what condition they are in or what caused the sickness. The Centers for Disease Control and Prevention (CDC) is investigating.

There were 549 people on board Emirates flight EK 203, which landed at John F. Kennedy International Airport around 9AM ET. CDC officials and police were waiting at JFK to check on the sick passengers, and the plane was moved away from the terminal to a hardstand area. According to the pilot, some passengers were coughing and had fevers over 100 degrees Fahrenheit (37.7 degrees Celsius), reported WABC-TV.

The mayor’s office confirmed via Twitter that the plane has been quarantined and the CDC is investigating. There’s been some debate about how many people were sick. At first, NBC New York reported that 100 people fell ill on the plane. But Emirates Airline tweeted a statement that about 10 passengers were sick. “On arrival, as a precaution, they were attended to by local health authorities,” the airline said. “All others will disembark shortly.”

In a statement to The Verge, the CDC said that “approximately 100 passengers, including some crew on the flight complained of illness including cough and some with fever.” The CDC worked with local authorities and US Customs and Border Protection to take passengers’ temperatures and arrange transportation to local hospitals. “Passengers who are not ill will be allowed to continue with their travel plans, and if necessary will be followed up with by health officials,” the CDC said.

By early Wednesday afternoon, everyone was off the plane, Eric Phillips, the press secretary for New York Mayor Bill de Blasio, tweeted. The latest count is that 11 were taken to the hospital, according to the CDC. That includes three passengers and seven crew members, Emirates tweeted. Everyone else was allowed to leave, the CDC said — but the source of the illness is still a mystery. “Health officials are processing tests now to determine the cause,” Phillips said. “Symptoms still pointing to the flu.”

Updated September 5th, 2018 1:30PM ET: Updated to include the most recent count of sick passengers.

Updated September 5th 7:21PM ET: Updated with most recent numbers.