Volodymyr Zelensky has called on any Ukrainian in Russian-occupied territory conscripts to “sabotage” the army from within if they are conscripted.
Speaking on Friday, Mr Zelensky condemned the referendums being held in four occupied regions - Luhansk, Kherson and partly Russian-controlled Zaporizhzhya and Donetsk.
Voting began yesterday on whether occupied regions of Ukraine should become part of Russia, in referendums that Kyiv and the West condemned as an illegitimate and a rigged attempt by Moscow to annex areas in the east and south.
The voting, overseen by Moscow-installed authorities and scheduled to run until Tuesday, is almost certain to go the Kremlin’s way.
"These are not just crimes against international law and Ukrainian law, these are crimes against specific people, against a nation," Mr Zelensky said.
"Hide from Russian mobilisation in any way you can. Avoid draft orders. Try to move to the territory of free Ukraine," he added, urging those who did end up in the Russian armed forces to "sabotage," "interfere" and pass on intelligence to Ukraine.
Mr Zelensky switched from speaking Ukrainian to Russian to directly tell Russian citizens they were being "thrown to their deaths".
“You are already accomplices in all these crimes, murders and torture of Ukrainians," he said.
“Because you were silent. And now it’s time for you to choose.
“For men in Russia, this is a choice to die or live, to become a cripple or to preserve health. For women in Russia, the choice is to lose their husbands, sons, grandchildren for ever, or still try to protect them from death, from war, from one person.”
Russian-installed authorities in the Kherson region said residents of a small Moscow-controlled area of the neighbouring Mykolaiv region also will be able to vote.
Ukraine and the West have denounced the vote as a sham and an illegitimate step toward annexation of a large slice of the country from the Russian border to the Crimean peninsula.
A similar referendum took place in Crimea in 2014 before Moscow annexed it, a move that most of the world considered illegal.
Election officials planned to bring ballots to homes and set up makeshift polling stations near residential buildings in the first four days of voting, according to Russian-installed officials in the occupied regions. Russian state TV showed teams of election officials yesterday going to residential neighbourhoods, with one such group accompanied by a police officer carrying a rifle.