"The airport is facing a threat," Carmen Surber, spokeswoman for the local Zurich police, told AFP, declining to specify the nature of the threat.
Check-in areas 1 and 2 and arrivals hall 2 were closed late yesterday but there were no flight cancellations, she added.
Passengers were being redirected to other check-in desks and suffered only minor delays.
There was a heavy police presence at the airport.
Several local media outlets said the authorities had received an anonymous tip about a bomb.