Around 15,000 runners were due to take part in the race on Sunday.
Large queues have formed for a running race in London after swathes of runners did not receive their bib numbers.
Around 15,000 runners were due to take part in the Vitality London 10km race on closed roads around the capital on Sunday.
Queues of participants waiting for replacement numbers snaked through Green Park, with the reason behind the delay unknown.
The first wave of runners was due to set off at 10am with the rest heading off in staggered starts, but organisers were having to hold them back.
A London Marathon Events spokesperson told the PA news agency: “We’re aware there are a number of people who haven’t received their numbers, so we’re issuing replacement numbers as fast as we can at Green Park.”
Anthony Bailly, 33, an IT project manager from Haringey, north London, said he had been waiting since about 8.35am.
He said: “Not much is being told to us, other than an ask to split into various numbers of queues, but it’s pretty much a free-for-all now.
“They have been calling people forward based on their start time, but people are reluctant to move to the priority queue because it’s starting to get longer than the queue we’re already in.”
The route starts on The Mall and travels past landmarks including Admiralty Arch, St Paul’s Cathedral, the Bank of England, Somerset House, Big Ben, the Houses of Parliament and Westminster Abbey, before finishing in front of Buckingham Palace.
Notable participants include British-Iranian dual national Anoosheh Ashoori and Richard Ratcliffe, the husband of Nazanin Zaghari-Ratcliffe, as well as Dame Barbara Windsor’s widower Scott Mitchell and EastEnders actor Jake Wood.
