Police were trying to determine why the truck left the road and careered down a dyke at about 7pm (6pm BST) in the town 20 miles south of Rotterdam, the Guardian reported.
Police said in a statement said that the driver, a 46-year-old man from Spain, was arrested as part of the investigation and taken to a police station.
The cause of the crash was not immediately known. “For the time being, we are keeping all scenarios about the facts open,” the police statement said.
Photographs of the scene showed bunting hanging between trees and chairs scattered around trestle tables.
A crane and tow truck were used to haul the crashed vehicle back on to the road late on Saturday.
Local mayor Charlie Aptroot said after visiting the scene: “My condolences go out to the victims, their families, eyewitnesses and first responders.”
He added that he had spoken to many of the people at the scene and expressed “appreciation for the way in which people are there for each other.”