London 2012 organisers have promised a "full review" after thousands of empty seats were visible across various venues on the first day of competition.
Despite most events having long since sold out, there were rows of empty seats visible at the swimming heats, the gymnastics, the volleyball and the dressage in Greenwich Park.
The London 2012 organising committee said it appeared that most of the empty seats were not sold to members of the public but were in "accredited" areas meant for members of the "Olympic family".
They include international federations, national governing bodies, athletes, International Olympic Committee officials and non-tabled media positions.
At the morning swimming heats featuring Michael Phelps and his US rival Ryan Lochte, there were an estimated 500 empty seats in one block alone.
And at the morning session of the gymnastics, at which Louis Smith and the rest of the British team appeared, there were more than 1,000 empty seats despite prospective ticket buyers being told it was sold out.
At the volleyball at Earl's Court, around a quarter of the seats at the 15,000 capacity venue were empty.
Andy Reed, a former MP and now director of Sports Thinktank, said there were "so many [empty] seats at the volleyball - really disappointed for so many who wanted to be there".
At the dressage in Greenwich Park, the arena was usually no more than two thirds full - but that could also put down to the fact that many people were dipping in and out of the action.
At the football, which is a different case in that there are far more unsold seats, there were vast swathes of unsold tickets for the women's matches at Cardiff's Millennium Stadium and Glasgow's Hampden Park.
During the sometimes controversial ticketing process, during which 6.6m of the 8.8m tickets were made available to members of the public, organisers repeatedly highlighted the lengths they were going to make sure there were no empty seats.
They said they wanted to avoid the situation that occurred in Beijing and at other Games, where even at sessions that were officially sold out there were large swathes of empty seats – particularly for morning heats.
The problem tends to be caused by IOC stipulations that retain a certain number of seats for officials, athletes, international federations and other accredited individuals. It can be particularly acute on the morning after the opening ceremony, which on Friday finished close to 1am.
In the vast majority of the venues, at least a fifth of seats are reserved for sponsors, officials, the media and the "Olympic family". In the most popular sessions, such as the opening ceremony and the 100m final, the proportion is closer to half.
"There were some empty seats in some venues, others were packed to the rafters. We are going to find out who should have been in those sections and why they weren't. We will deliver a full end of day report," said a Locog spokeswoman.
But those thronging the Park yesterday who had been unable to get into the venues to watch any live action were critical of the empty seats, which can also be highly embarrassing if shown on television.
"I think it's terrible, especially when so many people want a ticket. There should be less seats for officials," said Sharon Beers from Portsmouth.
Others said that given the frustration of the ticketing process, which started with a heavily oversubscribed ballot but ended with some of the most expensive tickets still remaining and 500,000 football tickets removed from sale, all venues should be full.
"We tried every single time to get tickets and all we cold get were tickets that got us into the Park. I'm less than happy with that situation, when you think of the amount of time we wasted trying to get tickets," added Susan Stoker from Hythe in Kent.
Organisers have talked in the past about running a Wimbledon-style ticket recycling scheme that would allow them to resell unused tickets to those already on the Olympic Park. They said they were still looking into how the logistics of such a scheme might work.
They also said they had been "very clear" with sponsors that any tickets they took up under the terms of their contract, which must be paid for separately, needed to be used.
The situation will be carefully monitored over the coming days and organisers are set to make changes if seats are being regularly unused.
Ironically, given the issues with empty seats, there were also reports of hundreds of people having to queue to enter the Aquatics Centre in the morning.
Locog chief executive Paul Deighton has talked in the past of his determination to avoid any empty seats, limiting the length of sessions and holding seminars with sponsors to underline the importance of only taking tickets they can use.
He introduced a so-called "fans in front" policy to try and ensure vibrant atmospheres in every venue.
"It is about full venues and, within those full venues, having people that look like they want to be there; and accessibility and, somewhere in that, that is where we will come out. I am absolutely committed," he told a parliamentary committee last year.
But even in those venues that were not quite full, those who were there described a vibrant atmosphere as hundreds of thousands of people turned out to watch the first day of action.
Mike Osey from Southampton, waiting to see if there were any tickets available at the public box office in the park, said people should be wary of making too much of the issue.
"This is superb, it's wonderful, it's working. Of course it would be better if they were resold but in the scheme of things it's a minor thing," he said.
