The alarm came to the police at 02.52 during the night towards Sunday.
- We do not know what happened, we are investigating it, we are questioning witnesses and so on to bring clarity, says Sylvia Oldin, duty officer at the Stockholm Police, just before five in the morning.
The area has been cordoned off and technicians are on their way to the site.
A preliminary investigation into attempted murder has been launched.
There are no suspects yet.