Amsterdam's Schiphol Airport has suddenly boosted its security in a move authorities there have linked to the "national threat level," snarling traffic as military police checked cars coming to drop passengers off.

The airport has not reported any delayed flights but authorities said Saturday that extra security would be "visible and noticeable."

Saturday is one of the busiest days of the year for Schiphol airport, as many people start their summer holidays and the Dutch Olympic delegation is set to fly out to Rio de Janeiro for the 2016 Summer Olympics.