Eight Dutch nationals, including two boys aged 13 and 15, were arrested in Antwerp suspected of acting as dockside drugs couriers.

Belgian police said the 15-year-old and a 24-year-old man were spotted in the harbour on Friday night. The following evening they returned to find the 13-year-old and a 22-year-old man trying to retrieve drugs from a container.

A search of the container revealed 58kg of cocaine in a cold storage area. Police said the drugs had been destroyed.

On Sunday evening four people – a 21-year-old woman, two men aged 18 and 19 and a juvenile – were arrested at the same spot.

“In view of the fact that all the offences took place in the vicinity of quay number 1624, the individuals were possibly looking for the confiscated drugs,” a spokesman for Antwerp police said.

The adults were arrested and will appear in court later. The youths were transferred to the youth justice division in Leuven.

The number of drug seizures in Antwerp and Rotterdam has dropped since the turn of the year. Police believe some traffickers may have transferred their operation to Spanish and French ports after surveillance was stepped up.