Armed police swoop on Dutch airport after terror tip-off

Armed military police launched a security sweep at Rotterdam airport on Thursday after receiving an anonymous tip-off about a possible terror threat.

Officers carrying machine guns and wearing bulletproof vests checked and searched some cars and buses arriving at the airport.

An investigation was "immediately launched" after "an anonymous message indicating a possible threat at Rotterdam The Hague Airport" was received, the police said in a statement.

"Certain extra security measures, both visible and invisible, are being put into place," the statement said, adding that Rotterdam mayor Ahmed Aboutaleb was being kept informed about developments.

In a short news conference, spokesmen for the military police said that air traffic was not being stopped to the airport.

Flights did not appear to have been affected in and out of the airport, which lies about six kilometres (three miles) north of Rotterdam, the busiest port in Europe.

By late Thursday the operation continued with military police spokesman Steven Comba telling AFP "there has been no change in the situation".

Comba said a decision to scale down the operation would be taken by Aboutaleb in conjunction with prosecution and police chiefs in the city "but that has not been done yet".

Police also scaled up their searches of vehicles coming into the airport after dark, Dutch public broadcaster NOS said, adding it was believed the tip-off came via an anonymous phonecall.

The Netherlands has been on high alert since the Paris attacks a year ago, and on Monday the Dutch counterterrorism agency warned that jihadist fighters returning from Iraq and Syria amid an offensive against the Islamic State group could increase the risk of a terror attack.

Earlier this year a drunk Polish man sparked a late-night scare at Amsterdam's Schiphol airport by falsely claiming to have a bomb in his backpack.

Police partially evacuated the airport -- one of Europe's busiest travel hubs -- during that incident, which came just three weeks after the March 22 attacks on Brussels airport and metro left 32 people dead and hundreds wounded.