People in the Netherlands are voting on the European Union constitution, just three days after a "No" vote plunged France into crisis.
Many Dutch are unhappy with the government and the economy
Turnout is reported to have passed 30 percent, the level set by politicians for accepting the public verdict in this otherwise non-binding referendum.
The Dutch prime minister appealed to the nation to back the treaty but polls predict 60% of voters will oppose it.
Many voting "No" share France's fears about expansion and a loss of identity.
'Not democratic enough'
Voting began at 0730 local time (0530 GMT) on Wednesday. Results are expected hours after polls close at 2100.
Christian Democrats (CDA), largest government party, plus coalition partners VVD and D66
Labour (PVDA) and Green Left opposition parties
Right-wing Pim Fortuyn party
ChristienUnie and SGP, Christian parties
The BBC News website's Stephen Mulvey in Amsterdam says he saw brisk voting early on, and a steady trickle throughout the morning.
The mood has been generally calm, with little evidence of political activity outside polling stations, he says.
Nico Smyders told the BBC he had voted "No" in part to register his opposition to the current Dutch government, but also to express his concerns about the treatment of small countries in Europe.
"I am for the European Community," he said, "but I don't think the big countries show enough respect for us."
Student Simon Catz voted "Yes" after heated discussions with his friends, who are divided between the two camps.
He says: "From what I have read the new constitution is not so much new laws as reaffirming old laws, and I am for that. I am satisfied with the EU."
Prime Minister Jan Peter Balkenende voted at his local polling station near Rotterdam.
"The future of the Netherlands is in Europe," he said on Dutch television late on Tuesday.
"I believe a 'No' vote is not in the interest of the Netherlands, not of Europe."
Correspondents say that a second vote against the constitution could create a snowball effect throughout the bloc.
The treaty - which aims to streamline EU institutions following the admission of 10 new members - has to be approved by all 25 member states before it can take effect.
In France, the decisive rejection of the document forced President Jacques Chirac to remove his prime minister.
He replaced Jean-Pierre Raffarin with Dominique de Villepin in a bid to prove he had listened and responded to voters' discontent.
In the Netherlands, any rejection of the constitution is unlikely to have the same impact as the Dutch vote is non-binding.
But the BBC's Geraldine Coughlan in The Hague says voters are unhappy about higher prices since the euro and discontented with the centre-right government.
ALREADY RATIFIED TREATY
Many also feel threatened by what they see as a superstate that will interfere with liberal policies such as those on gay marriage and euthanasia.
Others disagree with the swift enlargement of the EU, and oppose the possible inclusion of Turkey.
However, government and major opposition parties, making up 80% of the country's MPs, support the draft constitution in the belief that it will enhance Dutch influence in Europe.