Police have carried out sweeping raids in Denmark and Germany against suspected smugglers of doping agents and sexual stimulants, arresting six people and seizing over eight tonnes of drugs, authorities said Thursday.

The confiscated wares had a combined value of more than €11.5 million, the German customs investigation office in Hamburg said.

The police action was "one of the largest seizures of doping agents in Europe", it said in a statement.

Six people were arrested in the initial raids on June 13. The suspected smugglers were being detained in Denmark and face multiyear jail terms.

Danish police special forces moved on the main suspect after he had received a delivery of contraband in the Danish port city of Kolding.

In all, police searched six locations in Denmark and two in Germany, finding some 1.3 million pills of sexual stimulants.

Authorities raided another warehouse on July 7, seizing 780,000 vials and 3.3 million pills of various doping agents, as well as 450,000 pills of illegal narcotics and more than 580,000 sexual enhancement pills.

The gang is suspected of smuggling tonnes of drugs into the European Union over several years, generating "double-digit millions" in revenues. 

The group is said to have used the Danish-German border to conceal their activities. The contraband, likely to have been imported from "third countries", was then able to flow into the European market, Hamburg investigators said.

The move against the smugglers comes after a months-long investigation carried out together by Danish and German authorities with the support of the Eurojust justice cooperation agency.