More than 130 cyclists were arrested when they ignored warnings not to ride near the Olympic Park in east London as the opening ceremony was taking place, police said on Saturday.
They were part of a group called "Critical Mass" who hold a monthly cycle ride in central London that police believe had been joined by other riders planning to stage a protest.
"The procession usually attracts approximately 100 cyclists, but on this occasion around 400 to 500 people gathered near Waterloo (station)," Scotland Yard said in a statement.
"Officers believe this may have included other individuals or groups not normally part of the monthly procession."
The arrests came after they ignored warnings not to enter the Olympic route network or go near the stadium.
Critical mass groups stage monthly events - usually on the last Friday of the month - in over 300 cities around the world with the loose aim of "reclaiming the streets."
Protests against the London Games have been minor so far and usually directed against their corporate sponsors.