The Belgian customs service has uncovered tonnes of cocaine worth nearly €1.2 billion in Antwerp after police officers decrypted communications sent by criminal gangs, officials said Monday.

Federal police ran a two-year inquiry into organised crime which involved 500 million messages sent on Sky ECC devices sold by Canada-based firm Sky Global, the Antwerp prosecutor's office said in a statement.

A total of 27.64 tonnes of cocaine has been seized at the port of Antwerp since February 20, including 11 tonnes found in a container overnight on Friday.

The cocaine "can be directly linked to the Sky ECC case", the prosecutor's office said.

The chief executive officer and an associate of Sky Global were indicted in the United States in March for allegedly aiding drug smuggling.

The inquiry has seen 48 people arrested in Belgium and the recovery of guns, police uniforms and €1.2 million.

Investigations have spilled over into other countries including France where five people were charged at the end of March for selling encrypted telephones to drug traffickers.

"International contraband involving cocaine plays a big part in the intercepted messages," the statement said.

"From this data, dozens of drug shipments have been intercepted since February 20," it added. 

Inquiries into the people implicated were continuing.