Police arrested one suspect in connection with bomb threats made earlier Monday which led to the temporary evacuation of two Danish airports and two shopping centres.
The man, who is from the eastern town of Slagelse, will likely face a judge on Tuesday.
Aarhus and Roskilde airports were evacuated after police received near-simultaneous threats by telephone, news agency Ritzau reported. Threats were also sent by email to hospitals and universities.
Aarhus airport, which handled some 365,000 passengers last year, was reopened early on Monday evening.
Shopping centres in Roskilde and Slagelse were also cleared.
Sniffer dogs searched the affected premises, and several hours later the police gave the all-clear.
Copenhagen's main airport received an emailed threat, as did two universities and a hospital in the capital, but authorities saw the threats as "groundless" and did not order an evacuation.
Another hospital in Odense to the west of Copenhagen received a threat in its inbox, but there was no evacuation.