Crimeans have voted overwhelmingly to join former political master Russia as tensions soared in the east of the splintered ex-Soviet nation, the epicentre of the worst East-West crisis since the Cold War.

Partial results with more than half the ballots counted on Sunday showed 95.5 per cent of voters were in favour of leaving Ukraine, in the most radical redrawing of Europe’s map since Kosovo’s 2008 declaration of independence from Serbia.

Thousands in the regional capital Simferopol cheered the results, with the Russian national anthem ringing out on Lenin Square, later followed by celebratory fireworks.

“We’re going home. Crimea is going to Russia,” revelled Crimean leader Sergiy Aksyonov.

Alcohol-fuelled celebrations swept the mainly Russian-speaking peninsula with thousands waving Russian flags and singing Soviet-era songs as condemnation poured in from world capitals.

“We’re free of the occupation!” Lucia Prokorovna, 60, said in Sevastopol, strategic home to Russia’s Black Sea fleet.

“Ukraine was attached to Crimea like a sack of potatoes,” she said, carrying a giant white, blue and red Russian flag.

Ukraine’s new pro-European leaders and the West had branded as “illegal” the breakaway vote organised after Russian forces seized de facto control of the region and pro-Moscow authorities took power.

Russia’s move came after Ukraine’s pro-Kremlin leader Viktor Yanukovych was ousted in February after three months of bloody protests against his rule.

The choices facing voters were either to join Russia or go back to a 1992 constitution that effectively made Crimea an independent state within Ukraine. Retaining good relations with Kiev was not an option.

US President Barack Obama told Russian President Vladimir Putin in a phone call after the vote that a referendum that “occurred under duress of Russian military intervention, would never be recognised by the United States and the international community”.

He said the US and its European allies were “prepared to impose additional costs on Russia for its actions”.

Ukraine’s interim president Oleksandr Turchynov, who is not recognised by Russia and will be replaced after May 25 elections, said the results had been “pre-planned by the Kremlin as a formal justification to send in its troops”.

The European Union meanwhile said it would decide on Monday on sanctions against Moscow, including the possible seizure of the foreign assets of top Kremlin officials and travel bans for senior ministers.

“We reiterate the strong condemnation of the unprovoked violation of Ukraine’s sovereignty … and call on Russia to withdraw its armed forces to their pre-crisis numbers,” Brussels said in a statement.

British Foreign Secretary William Hague called the vote a “mockery” of democracy while France’s Laurent Fabius slammed a referendum “that took place under the threat of Russian occupation forces”.

But Putin – accused of orchestrating the vote as a way of seizing Ukrainian land and punishing its leaders for spurning closer ties with Moscow – seemed unmoved.

He told Obama that Sunday’s poll fell “completely in line with the norms of international law”, according to the Kremlin.

Moscow also said Putin intended to “respect” the outcome.

Crimea’s self-declared premier Sergiy Aksyonov earlier described the referendum as a “historic moment”, a sentiment echoed as the peninsula celebrated the outcome.

“We’ve won! We’ve turned the world upside down!” the head of the local parliament Volodymyr Konstantynov said from the stage in the Crimean capital.

Aksyonov said Crimea’s regional government would make a formal application on Monday to join Russia, following Sunday’s vote, where official turnout was put at over 81 per cent.

Crimean referendum commission chairman Mykhaylo Malyshev said his office had received no official complaints about violations. But accredited journalists including AFP were prevented from entering some polling stations in the port city of Sevastopol and in Simferopol.

Crimea’s indigenous Muslim Tatar community – deported to Central Asia en masse by Stalin – largely boycotted the referendum.

Others on the Ukrainian mainland pushed for their own right to decide on a Russian future, with around 4000 pro-Moscow activists rallying in the flashpoint industrial city of Donetsk and 6000 turning out in Kharkiv to support Crimea’s referendum and demand the right to their own referendum.

The two cities in Ukraine’s majority Russian-speaking east have seen a resurgence of violence in recent days with three people killed in clashes between nationalists and Russian supporters – the first fatalities since nearly 90 died in the week of carnage in Kiev that led to Yanukovych’s ouster last month.

In Kiev’s Independence Square – the centre of the protest movement that led to the toppling of the pro-Kremlin regime – the Ukrainian national anthem rang out as thousands gathered and militiamen roamed the streets.