Officers scuffled with several pro-cycling activists Friday as dozens of cyclists were blocked by police vans from proceeding, Scotland Yard said. No serious injuries were reported.
The cyclists were identified as members of a monthly cycling event called "Critical Mass" that normally passes through the area, but a police order had prohibited the group from travelling into the Olympic Park area in east London during Friday night's opening ceremony.
Police said they would give the precise number of arrests later.
Separately, a small radical Islam group had planned a demonstration outside the Olympic Park to expose what it calls "the evil of the Olympics" Friday, but the protest was cancelled for no stated reason last week.