A comedian with no political experience has beaten the incumbent Ukrainian president in the country's first round of voting.

Volodymyr Zelenskiy, who plays a fictional president on TV, held a comfortable lead over President Petro Poroshenko on Monday (March 31).

A vote which was deemed to be largely free and fair by the national electoral commission.

The pair beat 37 other candidates and are set to go head-to-head in a second round run-off on April 21.

Poroshenko called the result a "severe lesson", especially from younger voters, and urged their support in round two.

Propelled by his anti-establishment appeal, newcomer Zelenskiy must convince voters he is fit to lead a country that has been at war ever since protests in 2014 ejected a pro-Kremlin government and Russia annexed the Crimean peninsula.

Both Zelenskiy and incumbent Poroshenko face firmly west.

Neither wants to move Ukraine back into Russia's orbit.

Poroshenko has fought to integrate the country with the European Union and NATO while strengthening the military that is fighting Kremlin-backed separatists in Ukraine's east.

Pushing the Ukrainian language and helping to establish a new independent Orthodox church, he's cast himself as the man to prevent Ukraine again becoming a Russian vassal state.

But polls say that just 9 percent of Ukrainians have confidence in their national government.

That's the lowest of any electorate in the world.

Zelenskiy is hoping to change that - although his inexperience and apparent lack of policy detail make Western officials and foreign investors wary.

And Poroshenko has warned that his rival's reliance on social media and jokes renders him unfit to represent Ukraine abroad, especially when taking on Russian President Vladimir Putin in international talks.