Part of Amsterdam's Schiphol airport has been closed after authorities discovered a suspected World War II bomb, a spokeswoman said.
Terminal C has been evacuated as a precautionary measure, she said, and flights were likely to be affected.
The terminal serves most European destinations.
A bomb disposal team is at the scene, but passengers are advised to check their flights before going to the airport.
The bomb was uncovered by workers digging outside the terminal building, reports said.
"This will have a big impact. We can park planes somewhere else to some extent but at some point it will lead to cancellations or delays," the spokeswoman said, according to Reuters news agency.
Schiphol was used as a military airfield by Nazi Germany during the 1939-45 war, and was often attacked by allied bombers, Dutch media said.
It is now one of Europe's busiest airports, handling some 48 million passengers every year.