The contest to run the British capital has pitted Labour Party's Sadiq Khan, tipped to win the race, against Conservative Zac Goldsmith.
Labour Party's Sadiq Khan is on course to become the first Muslim mayor of an EU capital as voters in London went to polls on Thursday following a campaign marred by charges of anti-semitism and extremism.
The fight to run the British capital has pitted the Labour Party's Khan, 45, who grew up in public housing and is the son of a Pakistani bus driver, against Conservative Zac Goldsmith, 41, the elite-educated son of a billionaire financier.
Khan voted early in his multi-ethnic constituency of Tooting in south London while Goldsmith cast his ballot in the posh Richmond neighbourhood west of the city centre.
Mayors of London, which is home to the City financial district, are responsible for areas such as policing, transport, housing and the environment.
London is the top prize in local elections being held across Scotland, Wales and northern England, and there was little let-up in the accusations against Khan, who has a big lead in opinion polls, as campaigning ran into its final hours.
During a heated parliamentary debate on Wednesday, British Prime Minister David Cameron accused Khan of sharing "a platform with an extremist who called for Jews to drown in the ocean".
Labour Party leader Jeremy Corbyn in turn accused the Conservatives of "smearing" Khan. He said one of the men Cameron had accused Khan of sharing a platform with, had also been close to Goldsmith.
Khan, who would be London's first Muslim mayor, says he has fought extremism all his life and that he regrets sharing a stage with speakers who held "abhorrent" views.
Khan, a former human rights lawyer, has also had to distance himself from Corbyn after a row over anti-Semitism.
The Labour leader ordered an inquiry into charges of anti-Semitism after suspending Ken Livingstone, a political ally and a former London mayor, for saying Adolf Hitler had supported Zionism.
Khan was quick to condemn the comments and on Tuesday told reporters in his final stump speech of the campaign at a venue overlooking the River Thames: "I've had lots of people contact me from the Jewish faith sending me their support".
The row has failed to dent Khan's lead in opinion polls, a situation the Labour Party would like to be replicated in Thursday's other local and regional elections.
Khan v Goldsmith
Despite the surface-level rancour, both Khan and Goldsmith accept that the sky-high cost of homes and the city's creaking transport system are the dominant issues for voters.
Of the 12 candidates, second preference votes for the top two are added on to determine the winner. Final opinion polls put Khan 12 to 14 points ahead on second preferences.
London's Evening Standard newspaper endorsed Goldsmith on Wednesday, as he spent the last day of campaigning on a 24-hour tour of the city.
"Of the two strong candidates, he has more compelling ideas on tackling pollution and congestion," it said.
During a visit to a street market in south London on Wednesday, Khan told AFP his rival had run a "negative, divisive and increasingly desperate campaign".
"I've had a positive campaign from day one, talking about how my experience, values and vision will lead to me being the mayor for all Londoners," he said.
The new mayor replaces the eccentric Conservative Boris Johnson, whose eight-year term in office included the London 2012 Olympics and the launch of a cycle hire scheme dubbed "Boris Bikes".
Out of London's City Hall, the fiercely-ambitious Johnson -- a leading figure in the EU referendum's "Leave" campaign -- is the bookmakers' favourite to become Britain's next prime minister.