Armed police have swooped on the Polish consulate in central Manchester after two men were reported acting "suspiciously".
Officers were scrambled to the offices – based in the 21-storey Manchester One building – at 10.35am on Thursday.
A helicopter circled the sky above as dozens of staff were evacuated from the tower.
One man was arrested at the scene but a manhunt has been launched looking for the second.
In a statement, Greater Manchester Police said: "Police received a report that two men had been behaving suspiciously in the Consulate General of the Republic of Poland on Portland Street."
It added: "One man has been detained and officers are continuing to make enquiries in the nearby area.
"Officers are working to ensure that the incident causes as minimal disruption to daily business as possible."
Writing on Twitter, one witness said: "Cop cars pulled up but no one seems to be doing anything. Officers carrying guns showed up earlier too.”
The consulate itself was not answering calls by early Thursday afternoon.
