At 02:00 the police and emergency services were alerted to an explosion in a residential area in Nykvarn, writes County newspaper Södertälje.
It is not known what has exploded or if anyone has been injured, but the police tell Aftonbladet that they have found two cars with sheet metal damage in a carport.
Police have cordoned off the site and the National Bomb Squad is reported to be on their way.