The London Marathon is this year poised to be the biggest in the race's history, organisers said.
A total of 40,382 people collected their race packs on Saturday, meaning the 37th event is on course to outstrip last year's record of 39,140 competitors.
Over the last four days, runners have been pouring into the London Marathon Expo at ExCel London to register for the challenge.
Many will be waved off on their 26.2-mile journey by the Duke and Duchess of Cambridge and Prince William, who are later expected to be seen cheering on from the sidelines.
The royal trio have become the face of this year's event after their mental health campaign, Heads Together, was selected as its official charity.
Hundreds of police officers will be on duty to keep around 800,000 spectators and runners safe, barely a month after crowds were targeted in the Westminster terror attack.
The races start at Blackheath and Greenwich Park from 8.55am and end on The Mall.