The incident occurred near the Crypto.com Arena and the Los Angeles Convention Center on the 1200 block of south Figueroa Street at around 5 p.m.
LAPD said a group of 30 to 40 bicyclists were asked to clear the area but then set off a firework inside a trash can, causing a significant fire.
Figueroa Street was closed between Pico Boulevard and 12th Street as authorities investigated the incident.
No one was taken into custody. No further details were immediately available.