Moscow could officially annex the regions - around 15 per cent of Ukraine - within days.
The Kremlin-installed governments of the four Russian-occupied areas of Ukraine have all declared victories in the so-called annexation referendums.
Authorities published claims that an unprecedented majority of residents said yes to joining Russia on Tuesday evening.
Moscow could officially claim the regions - around 15 per cent of Ukraine - within days. Russia's parliament has earmarked October 4 to consider annexation, according to Reuters.
The polls, which Russian President Vladimir Putin announced along with the partial mobilisation last Wednesday, have been blasted by the West as a sham.
In Kherson, the head of the voting committee put the "yes" vote at above 87%.
Luhansk authorities said 98.4% of people there had voted to join Russia. In Zaporizhzhia, a Russian-appointed official put the figure at 93.1%.
Denis Pushilin, head of the self-proclaimed Donetsk People's Republic, said 99.2% of participants in the region had voted to join Russia.
"The referendums are over. The results are clear. Welcome home, to Russia!" Putin ally Dmitry Medvedev, a former president who serves as deputy chairman of Russia's Security Council, wrote on Telegram.
Denis Pushilin, the head of the Russia-backed separatist Donetsk People's Republic, said that the next steps would be signing an annexation agreement that would be ratified by Russia's legislature.
In a remark that appeared to rule out further negotiations, Ukrainian President Volodymyr Zelenskyy told the UN Security Council by video from Kyiv that Moscow's attempts to annex Ukrainian territory will mean “there is nothing to talk about with this president of Russia (Vladimir Putin)”.
Hastily arranged votes had taken place over five days. The four occupied regions -- some partially under Russian control -- make up about 15% of Ukrainian territory.
Russian-installed officials took ballot boxes from house to house in what both Ukraine and the West said was a coercive exercise to create a legal pretext for Russia to annex the areas.
The Ukrainian outlets pointed out that the population figures Russian-installed authorities cite are incorrect since around 80% of the pre-war inhabitants have either left Ukraine as refugees or have become internally displaced in other parts of the country.
The rest of the final count is expected as early as Tuesday evening. Putin is poised to announce the annexation of the four territories as early as Friday, when he is scheduled to address the Russian parliament.
Earlier, Moscow has vowed to give annexed regions of Ukraine "full protection," which could also involve the use of its nuclear arsenal, as the legal pretext would let Putin and the Kremlin portray any Ukrainian attempt to recapture them as an attack on Russia itself.
Ukraine has repeatedly warned that the Russian annexation of additional territories would destroy any chance of peace talks seven months after Moscow launched its full-scale invasion of the country in late February.
The European Union have both labelled the referendums as illegitimate, while the UN insisted on the territorial integrity of Ukraine within its recognised borders in light of the incoming results.
Russian state-owned news agency RIA said the initial counts showed majorities ranging from 96.97% in the Kherson region, based on 14% of votes counted, to 98.19% in Zaporizhzhia, based on 18% of the count.
The majorities in the so-called Donetsk and Luhansk People's Republics were just under 98%, with 14% and 13% respectively of votes tallied.