Federal officials said Thursday a jetliner bound for New York was being held on the tarmac at San Francisco's airport because of an alleged phone threat.
Officials stopped American Airlines Flight 24, headed to John F. Kennedy International Airport, before its scheduled takeoff at 7:30 a.m. PST, the Transportation Security Administration said.
The TSA said passengers were being taken off the plane on at least five buses to be interviewed and re-screened.
"All passengers are safe and out of an abundance of caution, TSA requested the plane be moved to a remote location," TSA spokeswoman Suzanne Trevino said in a statement.
The FBI later determined that the telephoned threat wasn't credible, but in the wake of the 9/11 attacks and a series of airline scares in the past year, the incident still rattled nerves as it played out live on national TV.
Police were investigating who called in the hijacking threat and what their motivation might have been.
A passenger on board the flight tweeting as @cmckella sent an update at about 12:40 p.m. saying that the buses were arriving at the plane to take passengers back to the terminal for security rescreening. Another tweet from @cmckella showed the scene from inside the bus as passengers were taken from the plane.
American Airlines spokesman Tim Smith said the threat was phoned into local police. He said there were no hostages, but the TSA has moved the plane to a remote tarmac.
Another passenger on the flight said two people on the plane were taken away in handcuffs. Michael Kidd told The Associated Press he saw uniformed police officers handcuffing a young man and a young woman sitting in the back row. They were taken off the plane.
But a fellow passenger suggested the couple may have been targeted because of their appearance. Michael Anderson, 20, said he remembered seeing the couple as he was checking in for the flight to New York's John F. Kennedy International Airport and saw them carrying passports from Pakistan.
"It definitely seems like it was racial profiling, based on what they look like physically and the fact they are Pakistani. It seems like this was a false accusation," said Anderson, a Yale University sophomore who was heading back to school.
The couple declined to discuss the possibility that they may have been targeted because of their appearance. "Of course we're upset, but I guess we can't blame them," the woman told the AP. "They're just doing their job."
Kidd said he and his wife did not believe the couple had been racially profiled based on appearances alone. The man wore a Los Angeles Lakers jersey and the woman was wearing a beret, and they looked like typical Californians, he said.
FBI sources told NBCNewYork that no one had been arrested and the feds were simply taking people off the plane two by two, bringing them to a private room and interviewing them.
"The two passengers were taken off the plane separately, but we cannot discuss the specifics why," said FBI spokesman Joseph Schadler.
Passenger Randy Cohen, 50, of New York said he lived across street from the World Trade Center on Sept. 11.
Cohen said the atmosphere on the plane was generally calm even though passengers got little explanation about why the plane had been diverted. But he said rumors about a hijacking or bomb threat began floating around among passengers connected to the Internet. "It was like, man, this can't happen again," Cohen said.
At the same time, via its Twitter feed, American Airlines reassured a passenger sending out tweets from aboard the aircraft.
"Hang in there," the airline said, "the authorities are taking care of things."
There were 163 passengers and 11 crew members aboard the Boeing 767, Smith said. No injuries were reported.
Federal Aviation Administration officials referred questions to TSA.