The head of the referendum committee in Ukraine's Crimea region says more than 95 per cent of voters have approved splitting off and joining Russia.

Mikhail Malishev said the initial result came after more than 50 per cent of the ballots had been counted. Russian news agency, Interfax, said voter turnout had exceeded 80 per cent.

Sunday's vote was denounced by the West and the acting Ukrainian government as illegitimate.

According to a statement released by the Kremlin, Russian president Vladimir Putin told U.S. president Barack Obama, in a phone call, that the Crimean referendum complies with international law. Putin also expressed concern about Kyiv's failure to stamp out violence against Russian speakers in Ukraine.

"Vladimir Vladimirovich Putin drew attention to the inability and unwillingness of the present authorities in Kyiv to curb rampant violence by ultra-nationalist and radical groups that destabilize the situation and terrorize civilians, including Russian speaking population," the Kremlin said

He suggested European monitors should be sent to all parts of Ukraine because of the violence, which the Ukrainian authorities blame on pro-Russian groups. Russian parliament has given Putin the authority to use the armed forces if needed to protect compatriots in Ukraine.

The White House released a statement following the Kremlin's saying that Obama told Putin that the U.S. does not recognize the Crimean referendum. He also said that the situation could still be resolved diplomatically if Russian troops stop incursions in Ukraine. According to Obama, U.S. and European partners were prepared to "impose additional costs" on Russia for violating Ukraine's sovereignty.

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.

"It may take up to five days to ratify the referendum," said the CBC's Susan Ormiston from Simferopol, the capital of Crimea. "They may introduce the ruble as soon as Tuesday...They have to look all kinds of national institutions like railways and water and gas infrastructures. Crimea doesn't have a lot of those. They come mostly from Ukraine, so Russia will have to negotiate deals."

The speaker of Crimea’s regional assembly said on Sunday that Moscow’s response to the referendum will be fast.

Opponents of secession appeared to largely stay away Sunday, denouncing the vote as a cynical power play/land grab by Russia.

Sunday's vote is taking place several weeks after Russian-led forces took control of Crimea, a predominantly ethnic Russian region. Its residents say they fear the Ukrainian government that took over when pro-Russia President Viktor Yanukovych was ousted last month will oppress them.

Since Yanukovych fled to Russia, Crimea has come under control of local militia forces, as well as heavily armed troops under apparent command from Moscow.

Crimea's pro-Russia authorities say that if Ukrainian soldiers resolutely occupying their garrisons don't surrender after Sunday's vote, they will be considered "illegal."

Ukrainian forces 'not going anywhere'

Ukraine's acting defence minister, Igor Tenyuk, said in an interview published Sunday by Interfax that "this is our land and we're not going anywhere from this land."

A woman casts her ballot at a polling station in Sevastopol, Ukraine. Many against secession stayed away from the vote. (Andrew Lubimov/ Associated Press)

In Kyiv, the CBC's Margaret Evans says the mood has turned dark.

"I would say there's a deepening sense of gloom here for many people," she told CBC News on Sunday. "For many people, they have gone through so much. They brought down this government...They are preparing for a war between Ukraine and Russia."

In Sevastopol, the Crimean port city where the Russian Black Sea Fleet is based under a lease agreement with Ukraine, enthusiasm for the referendum was high, with voters lining up outside polling stations before they opened.

I want to go home to Russia. - 66-year-old voter Vera Sverkunova

In Sevastopol, more than 70 people surged into a polling station within the first 15 minutes of voting.

Speakers blared the city anthem up and down the streets, giving Sevastopol a feeling of a block party.

A Russian naval warship stood blocking the outlet leading from the port to the open Black Sea."Today is a holiday," said one of them, 66-year-old Vera Sverkunova. Asked how she voted, she broke into a patriotic war song: "I want to go home to Russia. It's been so long since I've seen my mama."

A Russian military helicopter patrols the area as Ukrainian servicemen guard a checkpoint near the village of Strelkovo in Kherson region adjacent to Crimea. (Valentyn Ogirenko/Reuters)

At a polling station set up inside a historic school building in downtown Sevastopol, Vladimir Lozovoy, a 75-year-old retired Soviet naval officer, began tearing up as he talked about his vote today. Other voters cried out "Well Done! Hurrah"

"I want to cry. I have finally returned to my motherland. It is an incredible feeling. This is the thing I have been waiting for for 23 years and finally it has happened," he said.

Crimea's large Tatar Muslim minority opposes annexation to Russia.

Referendum a 'tragedy,' says Tatar minority

The referendum "is a clown show, a circus," a leader of the Crimean community, Refat Chubarov, said on Crimea's Tatar television station Sunday. "This is a tragedy, an illegitimate government, with armed forces from another country."

There are two questions on the referendum:

“Do you support reunifying Crimea with Russia as a subject of the Russian Federation?”

“Do you support the restoration of the 1992 Crimean constitution and the status of Crimea as a part of Ukraine?”

”The ballot actually doesn't give an option to stay in Ukraine," said CBC's Susan Ormiston, reporting from Simferopol in central Crimea. "The second option is to vote for an autonomous Crimea ... so the result is almost decidedly clear that this part of Ukraine will vote to go for Russia today."

This second question refers to a constitution that asserts Crimea is an independent state and not part of Ukraine. Reference to autonomy within Ukraine was inserted at a later date.

About 300,000 Tatars live in Crimea and make up a Turkic ethnic minority of 12 per cent in a region where 58 per cent of the population is ethnic Russian.

With the recent shift in political leadership in Kyiv, away from Moscow's influence, Russian soldiers have been marking an X on the doors of Crimean Tatars to identity their homes.

Blue-and-yellow Ukrainian flags were nowhere to be seen around the streets of Simferopol; red, white and blue Russian and Crimean flags fluttered around the sidewalks, city buildings and on many cars.

Some residents in Crimea said they feared the new Ukrainian government that took over when President Viktor Yanukovych fled to Russia last month would 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 Simferopol.

Ukraine's new prime minister insisted that neither Ukraine nor the West would recognize the vote.

"Under the stage direction of the Russian Federation, a circus performance is underway: the so-called referendum," Prime Minister Arseniy Yatsenyuk said Sunday. "Also taking part in the performance are 21,000 Russian troops, who with their guns are trying to prove the legality of the referendum."

As soon as the polls closed, the White House again denounced the vote. In Donetsk, one of the main cities in eastern Ukraine, pro-Russia demonstrators called Sunday for a referendum similar to the one in Crimea. The final results of the vote are not expected until Monday