"We are now investigating a suspicious situation aboard an aircraft at Schiphol", said the Marechaussee, a branch of the Dutch military tasked with protecting airports and borders.
Military police said the incident involves a "suspicious situation" on board a plane.
Schiphol airport is one of the world's busiest hubs, with more than 70 million passengers passing through each year.
Police and ambulances have been deployed near the aircraft, witnesses said.
He declined to name the airline involved or provide further details. This has not been confirmed by official authorities.
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Photos shared on social media show areas of the airport cordoned off with police tape.
The incident is reportedly taking place on board an Air Europe plane to Madrid with at least 27 people thought to be on the flight.
Dutch newspaper De Telegraaf has reported that an air ambulance is now at the scene.
The airport had initially declared a "serious situation that can have a major impact on the population", the Dutch news agency ANP reported. The investigation on the plane continues, they said. "We keep you posted".
An arrest team was called to the scene, and the D concourse was partially evacuated, according to Nu.nl.