A man has been arrested after a bottle was thrown on to the track seconds before the start of the men's 100 metres final at the Olympic Stadium.
A Metropolitan Police spokesman said a man had been heard shouting abuse and was then seen throwing a bottle.
The suspect is being held in police custody at an East London police station on suspicion of causing a public nuisance.
The bottle landed behind the sprinters (pictured top), coming to a halt a few feet behind Jamaican Yohan Blake, the eventual silver medallist, in lane five.
The sound of the item landing just behind athletes, including eventual winner Usain Bolt, could be heard on video footage just after the starter told the runners to "set".
United States athlete Justin Gatlin, who won bronze, said the bottle had been a "little distraction".
Nobody was injured and the event was not disrupted, police confirmed.
Speaking after the race, Gatlin said: "I didn't know what it was, but when you're in those blocks and the whole stadium's quiet you can hear a pin drop."
Gatlin said the incident had not affected the race: "You just have to block it out and go out there and do what you got to do.
"You can't complain about that, the race went on and it was a great race."
Bolt, from Jamaica, told reporters he had been unaware of the incident and said: "I don't know who would have done that."
Blake added: "I was so focused on just running to the line I didn't see anything."
Dutch judo bronze medallist Edith Bosch claimed on Twitter that she had "beaten" the person who had thrown the bottle.
She said: "A drunken spectator threw a bottle onto the track! I HAVE BEATEN HIM... unbelievable".
One spectator wrote on Twitter: "Man in front of me threw bottle onto track just at start! Had to be wrestled off..."
Another said: "So a drunk p---- actually threw a bottle onto the track as 100m started! He got punched by Dutch judo bronze medallist Edith Bosch tho".
"A man was arrested inside the Olympic Stadium on suspicion of causing a public nuisance on the evening of Sunday, 5 August," said a Scotland Yard spokesman.
"The man had been heard to shout abuse and then throw a plastic bottle on to the track immediately prior to the start of the men's 100m final.
"He remains in custody at an East London police station."
A London 2012 spokesman commented: "We are aware of the incident and are looking into it."
By Mike Rowbottom at the Olympic Stadium in London