Spanish police had tipped the Dutch to potential danger at the venue known as Maassilo where California band Allah-Las was set to play, but a judicial source in Spain told Reuters there was no link to the attacks in Spain last week.
"The investigation is ongoing and we are questioning the man," police spokesman Gijs van Nimwegen said. "We are working to determine his identity."
The van contained "a couple" of gas canisters and the man's driving had been "conspicuous" he said, declining to comment on Spanish police reports he had been drinking alcohol.
The Spanish source said late Wednesday that the tip resulted from an investigation by the Spanish Civil Guard that had been under way for some time and had no direct relation to the two vehicle attacks in Barcelona and Cambrils in Catalonia that killed 15 people.
Rotterdam Mayor Ahmed Aboutaleb told a news conference late Wednesday it was also not clear whether the threat tip and the detection of the van were connected. He warned against "swift conclusions" while noting the white van had Spanish license plates and had been flagged for circling near the concert venue.
"It would be wrong at this moment to pile up these facts and conclude ... there was a plan to attack with gas bottles," Aboutaleb said.
Spanish news agency Europa Press, quoting Spanish anti-terrorist force sources, reported that the Spaniard arrested in Rotterdam had, in principle, no link to jihadist terrorism. The gas canisters in his vehicle were apparently for domestic use, it said.
Police said the concert was canceled at around 7 p.m., shortly before doors were to be opened for guests. No one was hurt and only one suspect was in custody, Dutch police said.
The National Coordinator for Security and Counterterrorism's office said the threat level in the Netherlands was unchanged at "substantial", where it has been since 2013.
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