Terminal 2 of Copenhagen Airport in the Danish capital city was closed on Tuesday morning as police were investigating an "odd size luggage," the airport announced on its Twitter account.
It did not tell how long the airport would be closed and how many flights would be affected.
Copenhagen Airport is the busiest airport in Scandinavia, which served more than 29 million passengers in 2016 with its two terminals.
Security in European countries has been on high alert after a series of attacks hit populated areas such as airports and train stations in recent years.
Explosions at Brussels airport and metro systems on March 22, 2016 killed 32 people, and blasts struck Ataturk airport in Istanbul on June 28 in the same year, leaving 42 people dead and 239 wounded.
