The United States and Europe condemned the referendum as illegal, while Ukraine's new government called it a "circus" directed at gunpoint by Moscow.
The Crimea referendum offered voters on the strategic Black Sea Peninsula the choice of seeking annexation by Russia or remaining in Ukraine with greater autonomy, and secession was expected to be approved overwhelmingly.
Opponents of secession appeared to largely stay away today, denouncing the vote as a cynical power play and land grab by Russia. But the Crimean election commission reported turnout at 75 per cent even before the polls closed, well above the 50 per cent that would make the referendum binding.
More than 70 people surged into a polling station in the city within the first 15 minutes of voting today.
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"Today is a holiday!" said 66-year-old Vera Sverkunova, breaking into a patriotic war song: "I want to go home to Russia. It's been so long since I've seen my mama."
A vote backing secession would not only leave Russia facing strong sanctions by the West but could encourage the pro-Russian sentiment that is rising in Ukraine's east and lead to further divisions in this nation of 46 million.
The referendum comes two weeks after Russian-led forces seized control of Crimea.
Locals say they fear the new Ukrainian government that took over when President Viktor Yanukovych fled to Russia last month will oppress them.
"It's like they're crazy Texans in western Ukraine. Imagine if the Texans suddenly took over power (in Washington) and told everyone they should speak Texan," said Ilya Khlebanov, a voter in the Crimean capital of Simferopol.
Ukraine's new prime minister insisted again today that neither Ukraine nor the West will recognise the referendum, which he said was conducted at gunpoint.