Emergency services were called out to 18 county administrative board offices across Sweden on Wednesday morning after they received envelopes containing a mysterious powder.

According to Swedish daily Aftonbladet, the first report was made at around 9am on Wednesday morning in Västerås - a city roughly 100 kilometres west of the capital city Stockholm.

Several subsequent reports were made from around the country in the following hours, spanning from Norrbotten in the north to Blekinge in the south.

Police and emergency services were called out to all affected offices, which were immediately closed and evacuated as investigations were launched.

According to Swedish public broadcaster SVT, two people in the city of Linköping have been taken to hospital by ambulance in connection with these events. One further person has been taken to hospital in the region of Blekinge.

A similar incident unfolded in Blekinge in 2015, when a mysterious powder was sent to public broadcaster SVT's regional offices. In that instance the powder was found to be harmless.

According to the latest reports by SVT, the results show that the powder was not dangerous, but there is currently no information as to what the powder may be. The hospitalisation was thus likely just a precaution.

Aftonbladet reported that one of the letters was sent by "Sveriges djuägare", Sweden's animal owners. The letter said that the administrative boards had misused their powers and that the animal protection/welfare unit should be closed.

This is a breaking story. Updates to follow.