Belgian police have arrested 140 people attempting to pick up consignments of cocaine in the port of Antwerp in the first five months of this year, already surpassing last year’s total.

Half of those detained came from the Netherlands, including 20 minors and the youngest was just 13 years old, broadcaster NOS reported. The youngsters are sent into ports to collect cocaine hidden in sea containers, sometimes hiding in containers until the coast is clear.

Belgian police and lawyers warn that many young Dutch suspects underestimate the consequences of being caught in Belgium, where adult offenders typically receive prison sentences of around 40 months. Minors can be detained in youth institutions for several weeks or months.

By contrast, first-time offenders in the Netherlands often face only community service or a suspended sentence.

“There is a clear rise in the number of Dutch teenagers, and they are getting younger,” lawyer Chantal van den Bosch told Omroep Brabant. “Many think they will be home the same evening. That is absolutely not the case.”

While arrests in the port of Rotterdam have fallen this year, Antwerp is seeing a surge. According to Belgian police, criminal gangs now favour smaller drug shipments and send more, smaller groups of youngsters into the port to pick up the contraband.

Improved security, with more surveillance and checks in the port area, has also increased the risk of being caught, officials say.