The bomb was discovered at around 8am (0600 GMT) during excavations with Antoinette Spaans confirming to AFP “it’s a bomb dating from World War II.”
“Some flights have been cancelled and a dozen others have been delayed,” she said after security personnel evacuated part of Schiphol’s Terminal C as a precaution, while explosive experts were dismantling the device.
Spaans added flights would be affected for the rest of the day.
A spokesman for the Dutch military police, tasked with border security, could not say how long it would take explosives experts to clear the bomb.
“We are awaiting word from them,” Martijn Peelen told AFP.
Between 120,000 and 140,000 passengers pass daily through Schiphol.
Unexploded bombs and sea mines dating back to World War II are regularly found by Dutch fishing trawlers or farmers ploughing their lands, sometimes with deadly consequences.
Three Dutch fishermen died in April 2005 when a World War II bomb exploded on the deck of a trawler in the North Sea after it snagged in a net, prompting the Dutch and Belgian navies to ramp up the hunt for old explosives.
Schiphol itself was bombed at least twice during the war: first by the Luftwaffe during the German invasion in May 1940 and again by the Allies in December 1943, Dutch media reported.