The Dutch government said on Wednesday it could not ignore the resounding "No" in a non-binding referendum on the European Union's association treaty with Ukraine, but that it may take weeks to decide how to respond.
Although the results were preliminary, they exposed dissatisfaction with the Dutch government and policy-making in Brussels - signalling a anti-establishment mood in a founding EU member weeks before Britain votes on membership.
There could also be far-reaching consequences for the fragile Dutch coalition government, which currently holds the rotating EU presidency and which has lost popularity amid a wave of anti-immigrant sentiment.
Exit polls indicated roughly 64 percent of Dutch voters voted "No" and 36 percent said "Yes". Although turnout was too close to call, early tallies indicated it was just ahead of a turnout minimum of 30 percent required for the vote to be valid.
"It's clear that 'No' have won by an overwhelming margin, the question is only if turnout is sufficient," Dutch Prime Minister Mark Rutte said in a televised reaction.
"If the turnout is above 30 percent with such a large margin of victory for the 'No' camp, then my sense is that ratification can't simply go ahead," Rutte added.
That sentiment was shared by Diederik Samsom, leader of the Labour Party, the junior partner the governing coalition. "We can't ratify the treaty in this fashion," he said.
A person familiar with internal EU discussions on how leaders in Brussels would respond said EU officials had been hoping for very low turnout that would disqualify or diminish the impact of a "No" vote.
The European Commission, the bloc's executive, will play for time, waiting for the Dutch government to suggest a way forward, the official said.
The political, trade and defence treaty is already provisionally in place, but has to be ratified by all 28 EU member countries for every part of it to have full legal force.
The Netherlands is the only country that has not done so.
Options include leaving the agreement in force provisionally, or drafting exemption clauses for the Netherlands. Nothing will happen in a hurry, not least to avoid giving any succour to Britain's "out" campaigners.
Rutte said the government would consult with parliament and European partners "step by step. That could take days or weeks."
Pollster Ipsos said the validity was still unclear with provisional turnout at 32 percent - above the threshold - but within a 3 percent margin of error.
The referendum, called by eurosceptic forces, was the first since a 2015 law made it possible to force through plebiscites by gathering 300,000 signatures on the Internet - a law which is already being criticised.
"It is an instrument for anti-establishment forces," said Cad Mudde, an expert on Dutch politics and populism at the University of Georgia.
"It looks like the Dutch people said no to the European elite and no to the treaty with the Ukraine. (This is) the beginning of the end of the EU," Geert Wilders, leader of the eurosceptic Freedom Party, said in a tweet.
"I hope that later, both in the United Kingdom and elsewhere in Europe, other countries will follow," he said earlier.
Dutch leaders campaigning for the treaty had said voting against it would also hand a symbolic victory to Russian President Vladimir Putin. They had feared a repeat of 2005 when the Dutch rejected the European Union constitution, also in a referendum.
But ignoring a clear "No" would be risky for Rutte's already unpopular government - which has lost further ground over Europe's refugee debate - ahead of national elections scheduled for no later than March 2017.