Can Modi be elected for a third time? Will Donald Trump make a comeback? Will anyone in Russia challenge Vladimir Putin?

With half the world heading to the polls in 2024, including Pakistan, and some 30 countries electing a president, here are five key elections to watch:

Modi's great power play

Nearly one billion Indians will be called on to vote in April-May when the world's most populous nation goes to the polls in an election in which Indian Prime Minister Narendra Modi and his nationalist BJP party are seeking a third term.

Modi's political career and success have been based on support from India's one-billion-plus Hindus and, critics say, stoking enmity towards the country's large Muslim minority.

Despite a crackdown on civil liberties on his watch, he goes into the vote as the clear favourite, with his supporters crediting him with boosting his country's standing on the global stage.

Trump-Biden rematch?

On November 5, tens of millions of Americans will choose a president in a contest that could keep incumbent Joe Biden in power until the age of 86.

Poll after poll shows that a majority of voters think the gaffe-prone Democrat is too old to be commander-in-chief, despite his likely rival, ex-president Donald Trump, making similar slip-ups at 77.

Disinformation looks set to be a feature of the campaign, a hangover from the last foul-tempered contest, which ended with Trump supporters storming the US Capitol to try to halt the certification of Biden's victory.

Trump goes into the Republican Party nomination contest as the clear favourite, despite multiple criminal trials hanging over him.

Biden's campaign suffered another blow after the Republican-led House of Representatives voted in December to open a formal impeachment inquiry into whether he profited unduly from his son's foreign business deals while he was vice president under Barack Obama.

Putin eyes six more years

A newly-confident Russian President Vladimir Putin, energised by his troops' success in holding their positions in Ukraine two years into the war, is hoping to extend his 24-year rule by another six years in the March elections.

On December 8, he announced he was running for a fifth term, which would keep him in power until 2030.

In 2020, he had the constitution amended to allow him to theoretically stay in power until 2036, which could potentially see him rule for longer than Joseph Stalin.

With the war in Ukraine used to lock up or silence dissenters and opponents, there is little chance of anyone standing in his way.

His long-time nemesis, Alexei Navalny, is serving a 19-year jail sentence.

EU test for populists

The world's largest transnational poll in June will see more than 400 million people eligible to vote in the European Parliament election.

The vote will be a test of support for right-wing populists, who have the wind in their sails after the victory of Geert Wilders' anti-Islam, anti-EU PVV Freedom Party in November's Dutch elections and last year's win for Giorgia Meloni's far-right Brothers of Italy.

Brussels can take heart, however, from Poland, where former European Council president Donald Tusk has returned to power on a solidly pro-EU platform.

First Mexican woman president?

A leftist former mayor of the capital and a businesswoman with Indigenous roots are both vying to make history in Mexico in June by becoming the first woman president of a country with a tradition of machismo.

Former Mexico City mayor Claudia Sheinbaum is running on behalf of outgoing President Andres Manuel Lopez Obrador's Morena party.

Her outspoken opponent, Xochitl Galvez, has been selected to represent an opposition coalition, the Broad Front for Mexico.