Police spokeswoman Kenia Reyes said the Critical Mass usually has about 3,000 participants and has been happening on the last Friday night of every month in Miami Beach, The Miami Herald said Saturday.
"They overtake the streets," Reyes said. "The first time I saw that, I'll never forget it. I was dumbfounded."
The group gathered at Government Place about 7:15 p.m. Friday and rode through city streets in a large loop that returned them to their starting place by about 8:45 p.m., Reyes said.
Similar rides happen in several cities across the United States as a way for bicyclists to gather and assert their right to ride on city streets.