The two rivals for the leadership of Fifa, Sepp Blatter and Prince Ali bin al-Hussein, have delivered final appeals to electors in a vote overshadowed by corruption allegations.
Mr Blatter said he would “shoulder the responsibility of the current storm” and vowed to bring change.
Prince Ali pledged to bring “a new dawn to break through the darkness”.
The vote in Zurich comes two days after seven senior officials were arrested there as part of a US prosecution.
Mr Blatter is expected to beat Prince Ali and win a fifth term at the congress.
Mr Blatter has faced calls to resign, including from UK Prime Minister David Cameron, who said in Berlin on Thursday that Mr Blatter should quit “the sooner the better”.
Fifa’s 209 members are now voting in a secret ballot on whether to give Mr Blatter, 79, another four-year term.
Prince Ali, 39, is the only challenger.
In the first round, a candidate must get 140 votes – two-thirds – to win outright.
If that is not achieved, there will be a second round requiring a simple majority.
Analysis: Matthew Kenyon, BBC Sport
If you read most of the world’s media, Sepp Blatter’s ability to hang on to power at Fifa is nothing short of miraculous.
After years of negative headlines, the frenzy has reached fever pitch in the wake of the US allegations of corruption – even though Mr Blatter himself has not been implicated. And running through all this is a theme – bemusement that much of the football world keeps voting for him.
Nowhere is Sepp Blatter’s support stronger than across Asia and Africa. So why are most of the representatives from those two continents preparing to vote for him again?
Here’s about as succinct an answer as you’re going to get – from the president of the Nigerian Football Federation: “Blatter feels Africa. What Blatter pushes is equity, fairness and equality among the nations.”
We’re talking about two things – the first is concrete investment, often literally so. The second is respect.
Prince Ali, in his address to the delegates, said that questions had been raised in recent days “about whether our Fifa family is morally bankrupt”.
He said: “There are no easy answers and no blame that can be cast that will wash away the stain that marks us all.
“Today is about the first step towards a process of change – a new dawn to break through the darkness,” Prince Ali added.
Mr Blatter said: “I am being held accountable for the current storm – so be it, I will shoulder the responsibility. I will take it upon myself and I want to fix Fifa together with you.
“At the end of my term I will be able to hand over a strong Fifa – one that is integrated and will have enough safeguards to not need political interventions.”
To applause from a large number of delegates, he said: “I would like to stay with you. I would like to continue with you.”
Mr Blatter, in office for 17 years, enjoys strong support in Asia, the Americas and Africa.
Prince Ali has the support of most of Europe.
The vote comes two days after seven top officials were held in Zurich in a US fraud inquiry that indicted 14 people.
They are accused of bribery, racketeering and money-laundering involving tens of millions of dollars since 1991.
The aim of the bribes was to influence the outcome of bids to stage football tournaments such as the 2010 World Cup in South Africa and the 2016 Copa America in the US, prosecutors say.
Swiss prosecutors have launched a separate investigation into the bidding process for the World Cup tournaments in 2018 in Russia and 2022 in Qatar.
Many of Fifa’s major sponsors, including Coca-Cola, Visa, Adidas, McDonald’s, Hyundai Motor and Budweiser, have expressed concern over the investigations.
What do you think about the addresses delivered by Sepp Blatter and Prince Ali bin al-Hussein? Who do you think is the right man for the job? Are you in any of the regions affected by the Fifa scandal? You can share your views by emailing.
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