A blast in a caisson on a beach in the southern Dutch province of Zeeland on Friday evening was caused deliberately using high explosives, police report.

The Defence Ministry’s bomb disposal unit, the EOC, have ruled out a Second World War bomb or mine as the cause of the explosion at Ritthem beach. The police have now taken over the investigation, and are calling for information from witnesses. Two cars were reportedly seen driving away from the scene at speed after the blast, and cartridges were found near the site of the explosion.

The blast in the caisson could be heard for kilometres. It left a three-metre crater and scattered fragments of concrete across the beach.

The watertight concrete caissons were used on the beach to repair damage to the dike caused by allied bombing in October 1944.