The chairman of the London Olympics, Sebastian Coe, insisted on Sunday that most venues were full of spectators as organisers faced a growing storm over blocks of empty seats at several venues.
Local organisers LOCOG and the International Olympic Committee said they were urgently investigating why there were rows and rows of unoccupied seats at venues including Wimbledon for the tennis and the Aquatics Centre, while British police were reportedly probing an alleged black-market scandal.
As organisers were overwhelmed with demand for Olympics tickets when they went on sale and thousands of people were left disappointed, the sight of unoccupied seats has sparked anger in Britain.
Coe said unoccupied seats at some venues were due to accredited officials still working out which events to attend and planning their timetable, but he said he had visited four events on Saturday which were full to capacity.
"Let us put this in perspective. Those venues are stuffed to the gunnels. The public are in there," Coe told journalists.
"There are tens of thousands of people at this moment within the accredited 'family' that are trying to figure out what their day looks like, where they are going to be asked to go to, frankly working out how you divide your time.
"Certainly this is not going to be an issue through the Games.
"This is not unfamiliar in the preliminary rounds."
Coe said however that local organisers LOCOG were urgently seeking ways of filling any empty seats. He said soldiers involved in the security operation were given spare seats at gymnastics events on Sunday morning.
Students and teachers from east London were also allocated seats at some unfilled venues.
A source told AFP the local organisers were "extremely frustrated" by the empty seats, and were working flat-out to find a solution.
Many fans pointed out that gaps were visible at the Aquatics Centre, normally packed to the rafters for the early swimming action.
In contrast, huge crowds lined the streets of London, where tickets were not required, to watch Team GB compete in the cycling road race.
Britain's culture minister Jeremy Hunt admitted the empty seats were "very disappointing" and suggested they could be offered to members of the public.
He added: "I was at the Beijing Games, in 2008, and one of the lessons that we took away from that, is that full stadia create the best atmosphere, it's best for the athletes, it's more fun for the spectators, it's been an absolute priority.
"LOCOG are doing a full investigation into what happened. I think it was accredited seats that belonged to sponsors, but if they're not going to turn up, we want those tickets to be available for members of the public, because that creates the best atmosphere.
"We are looking at this very urgently at the moment."
One angry punter at the Olympic Park blamed corporate ticket-holders for failing to take up their seats.
"It's not fair. There's thousands of people who would have got into that swimming pool to watch the races this morning and couldn't get in," he told BBC TV.
"They've (now) panicked about the political situation of the stadium being empty. We couldn't even get in but people were coming out saying how the stadium was half-empty.
"There were thousands of people stood outside wishing to go in."
Meanwhile, the Sunday Times newspaper reported that British police were investigating the alleged black-market sale of Olympic tickets by three official ticket agents covering the Games.
The newspaper said it had secretly filmed Olympic officials and agents offering to sell thousands of tickets for up to 10 times their face value.
Detectives from Operation Podium, set up by the force to tackle Games-related ticket fraud, launched the inquiry last week after studying more than 20 hours of recordings provided by the newspaper, the report said.
They will seek to question officials from the national Olympic committees of China, Serbia and Lithuania, it added.
Contacted by AFP, police refused to confirm that they were investigating the claims.
One of the most embarrassing sights was at Wimbledon, where the match between British hopeful Anne Keothavong and former world number one Caroline Wozniacki was played to a half-empty Centre Court on Saturday.
"Very surprised at amount of empty seats on Wimbledon Centre Court, especially as I applied for some! It can't be more than 50 percent full," wrote frustrated fan Alex Dover on Twitter.