The ballots seek approval for declaring so-called sovereign people's republics in the Donetsk and Luhansk regions, where rebels have seized government buildings and clashed with police and Ukrainian troops over the past month.

Ukraine's interim president has said that independence for eastern regions will destroy the country's economy. "This is a step into the abyss for the regions," Oleksandr Turchynov said in comments posted on the presidential website Saturday.

Polling stations opened at 8 a.m. (0500 GMT) and were due to close at 10 p.m. (1900 GMT). Referendum organizers said they expected a high turnout, even though the security situation remained unstable around much of the area where the vote was held.

There were no reports of fighting as voting got under way, but insurgents in the city of Slovyansk, which has seen some of the most violent clashes between pro-Russian militants and government forces in recent weeks, exchanged fire with Ukrainian troops on the outskirts of the city overnight. And the port city of Mariupol on the Sea of Azov has remained on edge after Friday's clashes, in which at least seven died.

Ukraine and the West have accused Russia of fomenting or even directing the unrest in the east, with the goal of destabilizing Ukraine or finding a pretext for invasion. Russia has rejected the accusations.

Russia's President Vladimir Putin had asked the referendums' organizers to delay the vote as he bargained with Western powers on conditions for defusing the worst crisis in relations between Russia and the West since the Cold War. The insurgents, however, have refused to heed his call.

At one polling station in a school in Donetsk, turnout was brisk in the first hour of voting. All voting slips that could be seen in the clear ballot boxes showed that the option for autonomy had been selected.

Many voters said they hoped the vote would help stabilize the situation.

"I just don't have the words to express what is happening in our country," said the 65-year old Liliya Bragina. "I have come so that there will be stability, so that there will be peace."

The polling station's head, Andrei Mamontov, said he was certain the vote would be fair and not marred by falsification.

"In this polling station, everything will be fine, but I can't speak for other polling stations," he said. "We have prepared everything, we have signed everything, we have done all the checks — everything should be legitimate and clean."

The hastily arranged ballots are similar to the March referendum in Crimea that approved secession from Ukraine. Crimea was formally annexed by Russia days later.

But organizers of Sunday's vote have said that only later will a decision be made on whether they would use their nominal sovereignty to seek full independence, absorption by Russia or to stay part of Ukraine but with expanded power for the regions.

Surveys by polling companies have indicated that a significant majority of people in Ukraine reject movements to break away parts of the country.

Ukraine's interim president said supporters of independence for the east "don't understand that this would be a complete destruction of the economy, social programs and general life for the majority of the population."

Turchynov and Ukraine's caretaker government came to power in February following the ouster of Russia-friendly president Viktor Yanukovych after months of protests in Kiev. Moscow and many in Ukraine's east denounce the new government as a nationalist junta and allege that it intends to trample on the rights of eastern Ukraine's Russian-speakers.

More than 30 people have been reported killed since Ukrainian forces began mounting offensives to retake some eastern cities now under control of the insurgents.