Police in southern Finland have said they suspect a particularly dangerous drug is circulating in the Porvoo area.

The substance appears to have been sold illegally in tablet form as benzodiazepine and ecstasy, police said in a statement.

"But because the actual composition of the substance is unknown, it poses a particular danger to life and health when ingested," Detective Inspector Freddie Cederlund stated in the press release.

He added that the currently available information on the substance is based on the police's own observations as well as details provided by users.