A proposal by Elon Musk on ending the Russia-Ukraine war has been slammed after the world's richest man posted his "solution" to Twitter.

The Tesla CEO claimed peace between Ukraine and Russia could be achieved by redoing "elections of annexed regions under UN supervision", with Russia to leave "if that is the will of the people".

In addition, he proposed that Crimea be formally recognised as part of Russia "as it has been since 1783 [until Khrushchev's mistake]", and that "water supply to Crimea" be assured.

Ukraine, under Musk's plan, would remain "neutral".

"This is highly likely to be the outcome in the end — just a question of how many die before then," Musk wrote on social media.

The billionaire's overly simplified take, which also featured a poll for Twitter users to vote "yes" or "no" on, was widely rejected and deemed completely impractical.

More than 63 per cent of people voted "no" in response to Musk's poll.

Ukraine President Volodymyr Zelenskyy shot back with a poll of his own, with the question, "Which [Elon Musk] do you like more? One who supports Ukraine [or] one who supports Russia?" More than 84 per cent of people voted, "One who supports Ukraine."

Ukrainian diplomat and lawyer Andrij Melnyk was more blunt, writing: "F**k off is my very diplomatic reply to you [Elon Musk]."

Russian dissident and former world chess champion Garry Kasparov blasted the US tech billionaire.

• Ukraine reclaims more territory in southern Kherson
• Biden vows Russia won't 'get away with' Ukraine annexation

"This is moral idiocy, repetition of Kremlin propaganda, a betrayal of Ukrainian courage and sacrifice, and puts a few minutes browsing Crimea on Wikipedia over the current horrific reality of Putin's bloody war," Kasparov wrote on social media.

Sergiy Kyslytsya, Ukraine's representative at the United Nations, wrote: "Next time I need a plumber I call [Elon Musk]. He doesn't do plumbing?! Then what the heck's the matter, why does he speak of international relations and international law? [By the way], a good plumber is better than Musk's second-hand opinions on illegally occupied territories of a foreign nation."

Russia invaded and annexed the Crimean Peninsula from Ukraine in 2014 in a move that was not recognised by the international community.

Russia staged referendums on the annexation of occupied territories of Ukraine in September this year. The United States, the European Union and the United Nations have condemned the annexations.

Illia Ponomarenko, a reporter at the Kyiv Independent and one of the most prominent journalists covering the war, wrote in response: "People - Elon Musk simply said something stupid on Twitter regarding a thing he has very little idea about. A failed sh**posting attempt deserves getting ridiculed into oblivion, but there's no point making an enemy out of him now."

Several of those who weighed in asserted it was inappropriate of Musk to use his platform of 107.7 million followers to present his wild theories.

The SpaceX founder was told it was unhelpful, and in some ways, made the situation worse.

"Elon, you've done so much good for Ukraine by enabling Starlink and providing thousands of terminals. As a fellow Aspie [person with Asperger's] I get that you're hyperfocused on this topic right now, but these polls and the tweets about bot attacks aren't helping – in fact, they enrage many Ukrainians," one respondent wrote.

Others agreed the solution to the war was not Musk's to determine.

"It's not for you to decide," one said, arguing the only way forward was for Russia to leave Ukraine and pay for its damages.

"The only possible way to peace is for Russia to completely withdraw from ALL Ukrainian territory, pay for the damage and crimes committed here, and acknowledge that we can join whatever alliance we want," they wrote.

Many were disturbed at Musk's apparent belief that Russia has a legitimate claim to the Crimea.

"You're under the mistaken impression that Russia has any claim to any of Ukraine," one Twitter user wrote.

Others said Musk's opinion on the matter was important.

"I think it is worthwhile to listen to what people like Elon have to say. Don't have to agree."

"His opinion is offered respectfully, as a possibility. Brainstorming principles say not to reject any ideas until there are many. A rejected idea can lead to the answer," one person said.

Many disagreed, saying it was disrespectful to suggest annexations of Ukrainian territory should be legitimised.

"You're trying to tell that to a soldier in the Ukrainian army who knows from his own personal experience what he is defending his country against: rape, murder, torture, theft, destruction. All that will continue in the territories that Russia occupies until they're defeated," one person said.

In a poll posted in response to Musk's, a Twitter user asked others if they thought the billionaire should "shut up".

More than 88 per cent of 21,380 respondents voted "yes", while just 12 per cent voted "no".

Musk's tweet came after chilling footage showed a Russian train loaded with vehicles and equipment appearing to be heading towards the front line in Ukraine.

Defence analyst Konrad Muzyka told the Sun the train was linked to a unit that operated a dozen central storage facilities for nuclear weapons.

"This is actually carrying kit belonging to the 12th Main Directorate of the Russian MoD," he said.

"The directorate is responsible for nuclear munitions, their storage, maintenance, transport, and issuance to units."

The expert stressed the video was not showing "preparations for a nuclear release".

He said however it was significant that it emerged after Ukraine warned of the "very high" risk of Russia using a tactical nuclear weapon.

- Brooke Rolfe, news.com.au