More than 300 police officers backed by two helicopters on Sunday mounted a massive search along Romania's Black Sea coast after 131 kilogrammes of cocaine washed ashore, police said.

Police spokesman Georgian Dragan told AFP that 14 boats and several frogmen were also involved in the unprecedented search operation for more packets of the drug, which began arriving ashore on Friday.

Romania's organised crime unit urged local residents not to open packets appearing on the beach "whose contents could put their lives in danger".

On March 20, more than a tonne of cocaine packed into 36 plastic bags apparently from the same shipment were found in a boat that capsized in the Danube delta. Two Serbians were arrested in connection with that discovery.

Around 200 more kilos were plucked out of the Black Sea last Tuesday, police said.

Prosecutors evaluated the cocaine's purity at 90% and said it was worth hundreds of millions of euros.

Romania is a key transit point for cocaine originating in Latin America destined for western Europe.

Romanian police seized a record 2.5 tonnes of cocaine from Colombia in the Romanian Black Sea port of Constanta in 2016, with an estimated value of €600 million.