THE HAGUE (AFP) - Dozens of heavily-armed military police swooped on Amsterdam's Schiphol airport late on Tuesday (April 12), evacuating part of the busy travel hub and arresting one man, triggering a security alert that was lifted after about four hours.

"Police have evacuated part of the airport plaza and the adjacent Sheraton Hotel and arrested one person amid a suspicious situation," spokesman Danielle Timmer told AFP, adding she had no further information.

Reporters showed heavily armed Dutch special military police, wearing balaclavas, patrolling the airport which has been on high alert since the March 22 attacks in Brussels. Passengers anxiously watched from behind security tape. Part of the airport was cordoned off for about four hours while a helicopter hovered overhead, until the alert was lifted at around 1.30am local time on Wednesday.

"The airport has been declared safe again," military police spokesman Alfred Ellwanger told reporters.

It remained unclear exactly what had triggered concerns, or who had been arrested, but Mr Ellwanger said nothing dangerous had been found in a search of the arrested man's luggage.

He had no further details about the arrested man, saying more information would likely be available later on Wednesday.

Mr Ellwanger told AFP that "around 9.45pm (3.45am Singapore time) a man was arrested on the square in front of the main entrance to the airport's plaza".

Britain's Daily Express newspaper reported that a suspicious package was found and bomb disposal robot was pictured at the airport at around 11pm local time.

Mr Ellwanger added that no flights were disrupted at the busy airport and trains were arriving as normal at the underground station which links the huge travel hub to the rest of the Netherlands.

It was not immediately clear how many people were evacuated when military police cordoned off the area, but Mr Ellwanger said there had only been a few departures or arrivals left for the day.

"All areas are accessible again. Tomorrow, flights will run as usual. Thank you all for your patience and understanding tonight," the airport said early Wednesday on its official Twitter account.

Earlier, the Twitter account had said: "Part of Schiphol is not accessible due to an incident. Police is investigating the matter. For now, air traffic has not been affected."

A spokesman reached by AFP for the 407-room Sheraton hotel, which is linked to the airport via a covered walkway, declined to comment.

"Nobody is telling us anything about what's going on. My car is in the parking garage and I can't get it out. I'm a diabetic and I need my insulin," said a 72-year-old Dutchman.

Witness Victor Pascual told CNN that people near him started running while he was in a shuttle bay, but he did not know what had happened.

He also said many people were stranded outside the terminal. "We have not been give any further information apart from to remain calm," he told CNN.

Airport officials over Twitter told CNN that they were still investigating the situation.

Schiphol's busy modern plaza and entrance is usually crowded with passengers and visitors many of them enjoying a meal at one of the many eateries, or perusing the shops, many of them selling upmarket clothes and cosmetics.

One person was also arrested at nearby Leiden railway station for raising a "false alarm", a spokesman for The Hague police told AFP, but she added that incident was not related to the Schiphol investigation.

Another person was arrested at Schiphol, but also unrelated to the incident, the police said.

There has been concern in the Netherlands about whether it could potentially be targeted in terror attack, due to its proximity to both Belgium and France. Dutch politicians have stressed that they are working to keep the country safe.

As a precaution, the government stepped up security at national airports and train stations and tightened controls on its southern border with Belgium in the wake of the Brussels attacks.

Dutch police carried out raids in Rotterdam last month, uncovering about 45kg of ammunition in one apartment linked to a foiled attack on France.

French suspect Anis Bahri was arrested at the flat in the southern port on March 27 at Paris' request, amid suspicions he was planning an attack in France for the Islamic State in Iraq and Syria (ISIS).

He is fighting his extradition to Paris, where he is wanted on suspicion of plotting the foiled attack with another man, Reda Kriket. Two Algerians arrested with Bahri have been remanded in custody in the Netherlands.

Schiphol, which lies just outside the Dutch capital Amsterdam, is one of Europe's busiest travel hubs with about 50 million visitors passing through each year.

Tensions have been high since the Brussels airport and metro bombings killed 32 people in neighbouring Belgium.

Like the November attacks on Paris, the March 22 bombings were claimed by ISIS.