The person was assaulted after what police described as an “altercation” on a bus in the Stockholm suburb of Husby. The offender then disappeared from the scene when the bus stopped at the next stop.
Police received news of the event at 12.55pm on Saturday and arrived at the scene along with an ambulance.
“We have several patrols in place working on this,” said Eva Nilsson, a spokeswoman for the Stockholm police.
“There was some kind of argument that went haywire,” Nilsson continued. “They did not appear to know one another.”
“We will look at the surveillance tape from the bus and will work with the witnesses,” she said.
“We have some information on the suspect, but that is all we are prepared to say.”
The victim was taken to hospital but their condition was not stated.
Husby gained notoriety in 2013 due to riots that spread to several other parts of Stockholm.
Husby also has the lowest income per capita of any district of Stockholm.