Five hundred people have been evacuated from a building in Stockholm following a potentially explosive chemical leak.

"There has been a discharge of gas in this room. It is probably the chemical toluene. In concentrated form it constitutes a fire and explosion hazard," police spokesperson Sven-Erik Olsson told Swedish tabloid Aftonbladet.

The leak started on the seventh floor of the building in premises used by a biochemical company, reported The Local.

Four people are being treated by paramedics after suffering dizziness and facial numbness, said police. The building has been sealed off by emergency services and officers in specialist protective equipment are attempting to identify the leaked substance.

The building in the north western Solna municipality houses the Karolinska Institute and the Royal Institute of Technology, as well as several companies. The district is also the location of the Friends Stadium, which in previous years has hosted football matches and the Eurovision Song Contest.