A bus with Spanish license plates and containing gas bottles was found near a concert hall where earlier on Wednesday a rock concert was cancelled due to a threat, Rotterdam's mayor said.
Ahmed Aboutaleb told a news conference it wasn't clear whether the threat and the bus were connected. The bus driver was taken into police custody for questioning, he said.
Police told Dutch news agency ANP the concert, which was to feature Californian band called the Allah-Las, was cancelled after a tip from Spanish police.
The 1000-capacity venue had already been evacuated when the van was found.
The Allah-Las, from California, say they chose the name because it sounded "holy", and aren't trying to offend anyone.
"We get emails from Muslims, here in the US and around the world, saying they're offended, but that absolutely wasn't our intention," lead singer Miles Michaud told The Guardian last year.
"We email back and explain why we chose the name and mainly they understand."
Reuters / Newshub.