“False alarm,” the airline declared on Twitter — but by then it was too late.

Military police officers, fearing a hijacking on Wednesday, had already swarmed onto the tarmac of Amsterdam’s Schiphol Airport, and air traffic controllers were scrambling flight schedules at one of Europe’s busiest air hubs.

But Air Europa, a Spanish carrier, said it was all a mistake. A warning system on one of its flights from Amsterdam to Madrid had been accidentally activated late in the day.

“Nothing has happened,” the airline said in a Twitter post more than an hour after the airport was partially shut down. “All passengers are safe and sound, and waiting to fly soon. We deeply apologize.”