Olympics venues are "stuffed to the gunnels" with sports fans, London 2012 chairman Lord Coe has insisted amid a row over empty seats.
He spoke after hundreds of seats were left unfilled on Saturday and Sunday morning at events including swimming, rowing, tennis and basketball.
"I don't think you will be seeing this as an issue, long-term through the Games," he said.
Meanwhile, GB swimmer Rebecca Adlington has won her 400m freestyle heat.
She is due to swim in the final at 20:18 BST.
Elsewhere in other Olympic developments:
- Paula Radcliffe admits her chances of appearing in the Olympic marathon next Sunday are "not looking good"
- Russia's Maria Sharapova gets her tennis campaign under way at Wimbledon
- Police say 16 people have been arrested over ticket touting at the Olympics during the past two days
- A huge puppet version of Lady Godiva begins its journey from Coventry to London on a purpose-built 50-seater bike as part of the cultural celebrations for the Olympics
- Zara Phillips said the crowds were "amazing" as she competed in the dressage
- The unidentified woman who joined the Indian delegation at the opening ceremony has been identified by Lord Coe as a volunteer performer who had got "slightly over-excited"
Lord Coe spoke out as the row mounted over unfilled seats in several Olympic venues.
At some venues, seats in the accredited "Olympic family" areas - reserved for groups including officials, sports federations, athletes, journalists and sponsors - have remained unfilled.
Empty seats "in the very earliest phases" of the Olympics were part of "the nature of that accredited area", Lord Coe told a press conference.
"[The ticket-holders] are trying to figure out how they're going to divide their time, what their responsibilities are, and how and when they get dragged to any number of venues," he said.
Organisers would fill some of the empty seats with servicemen and women, as well as local students and teachers, he added.
And they would sell more tickets - as they did with about 1,000 tickets on the London 2012 website on Saturday night.
He said a system had been introduced similar to the one used at Wimbledon, where people coming out of the stadium handed on their tickets so the seats could be made available to others.
Tickets are also given to sponsors and, on Sunday, Visa, British Airways and Lloyds TSB all said they had given the majority of their ticket allocations to customers through competitions and promotions.
Lord Coe added that sponsors "were turning up," adding that they would not be naming and shaming those who did not.
On Sunday, the BBC's Kevin Bishop, at the rowing at Eton Dorney, said the cheap seats were pretty full but opposite, next to the press seats in the main stand at the finish, there were several hundred empty seats.
Banks of empty seats could also be seen at Wimbledon's centre court and the Aquatics Centre on Sunday morning.
American Paul Fondie, who now lives in Kew, west London, said he was frustrated by the number of empty seats at the men's gymnastics at the O2 on Saturday.
He said he and his wife had not been able to take their six-year-old son because they could not get an extra ticket.
"It tainted my experience of the Olympics - it was our moment to come under the microscope and show that London can do it well."
BBC correspondent Andy Swiss said ticketing was a sensitive issue after many fans missed out and the empty seats were a problem Locog would be anxious to solve.
Meanwhile, Mansfield-born Adlington began her defence of the two gold medals she won in Beijing in the 400m freestyle heats on Sunday morning.
Her battle to hold on to her 800m freestyle title will begin with heats on Thursday morning before Friday night's final.
Cyclist Nicole Cooke is competing in the women's road race - the event in which she won Team GB's first gold at Beijing in 2008 - which began on The Mall at 12:00 BST and will finish there at about 16:00 BST.
But she could be forced to sacrifice her own gold medal hopes this time to be a support rider for teammate Lizzie Armitstead.
Andy Murray - who was defeated with his brother Jamie in the tennis doubles on Saturday - will play Stanislas Wawrinka in the singles at Wimbledon.
And Briton Ben Ainslie has begun his quest for a fourth Olympic gold medal as the first day of Olympic sailing begins at Weymouth Bay.
British teams are competing in basketball, handball, hockey, volleyball, water polo and the football on Sunday.
Meanwhile, the US basketball team - the most decorated in Olympic basketball - will begin their title defence against France later.