Annette Rieger, who works in the H&M building, told The Local.se the swarm was outside for about 3 hours Friday afternoon.
"I saw them all over the windows. They even got through the first level of glazing," she said. "My colleague was super scared because she is allergic to bees!"
Johan Jarbrant, chairman of the Stockholm Beekeepers Association, and a colleague moved the swarm to a more isolated location away from downtown Stockholm. Wearing protective clothing and brought up to the bees' level by a crane lift, they calmed the insects with smoke and loaded them in boxes.
Jarbrant said there were about 5,000 bees in the swarm.
Swarming is a normal part of the bees' life cycle, with hives dividing when there are two queens and one group takes off to find a new home.