Danish police are investigating a number of letters containing an unidentified powder and threats that were sent from Belgium to several food processing companies in Denmark.

Uffe Stormly of Denmark's National Police says the letters contained "a hazardous substance." Stormly declined on Wednesday to disclose details about the letters as the investigation was ongoing.

Danish media said the letters demanded a 30,000-euro ($33,735) ransom or their products would be infected.

Danish Crown, which describes itself as Europe's largest meat processing company, confirmed it received such letters. It said, citing information from authorities, that the letters had been sent to several food-processing companies in Europe.

The company said neither staff nor consumers were at risk.