The event has been overshadowed by the murder of Miss Honduras, 19-year-old Maria Jose Alvarado, shot dead with her sister in their homeland last month on the day she was due to travel to London.
Police in Honduras accuse her sister Sofia’s boyfriend of shooting them after seeing his partner dancing with another man at a party.
Whoever takes this year’s crown will travel to the violence-hit central American nation to build a school named in their honour.
Miss South Africa, 22-year-old medical student Rolene Strauss, is bookmakers’ favourite to win the title at 6/4.
Other contenders include Miss India, 21-year-old health awareness campaigner Koyal Rana, 21, who is highly tipped at 5/1.
The winner is due to be announced shortly before 1700 GMT.
Megan Young of the Philippines won the 2013 title in Bali, Indonesia. She is to co-host this year’s final — a first — and crown her successor.
“This year, we are in London and the show is modern, it’s fun, and totally fresh,” she said in her final interview in the role.
The 24-year-old has travelled to more than a dozen countries as Miss World but said putting it to good use in the aftermath of Typhoon Haiyan, which killed at least 6,300 people in her homeland, had been the most important moment of her reign.
The pageant at the ExCel centre is expected to be targeted by feminist protestors who argue that it degrades women and is old-fashioned.
They were rallying support on Twitter under the hashtag #missworldoldworldmisogyny.
“The sexist idea that women should be judged on the basis of their appearance influences the way that all of us feel about ourselves as women and the way that men view and treat women,” one of the groups backing the protest, the London Feminist Network, argued on its website. – AFP