The shipment was discovered on a lorry in Zwolle, in the Netherlands, after Dutch border officers intercepted it on Monday.
Some of the seized life jackets were found to be in children’s sizes.
Local authorities are now investigating the lorry’s 23-year-old driver, who was arrested on suspicion of offences related to people smuggling, the NCA said.
It added that the shipment had been initially sent to Italy after it was purchased, before being transported to the Netherlands.
The NCA said the seizure came as the result of a joint operation with Dutch and Italian authorities, as well as the UK Border Force.
“There is no doubt that this unsuitable equipment had been acquired by criminal networks who intended to use it for small boat crossings,” Mr Beer, the agency’s regional head of investigations, said.