They seemed particularly attracted to a truck at Geary Street between Mason and Taylor streets. It's not clear where they came from.
PHOTOS: Bees swarm area in downtown San Francisco
Owner Theron Kabrich couldn't believe his eyes. "Somebody on my staff called me downstairs to say 'there's something out here you've never seen before.' I've been on a Geary a long time, so that's a big claim," he said.
Kabrich said the bees seemed passive. "I could walk right through the cloud and the bees would part and they were still looking at that truck," he said.
Once the truck left the bees congregated on a parking meter. "Now the bees are lost, you can see them flying around, they don't know where the others went," Kabrich said
Kabrich said a beekeeper came by late Thursday afternoon to collect the bees.
As for the sight of so many of them just outside his business, Kabrich said only in San Francisco. "The most unique city in the world," he said.