Police emphasized that most of the protesters were peaceful. But there have been several splinter groups from the main protest that have been more aggressive, officials said.
LAPD Cmdr. Andy Smith said some demonstrators threw rocks and D-cell batteries at police near the corner of Washington Boulevard and 10th Avenue. Police responded by firing less-than-lethal rounds at the demonstrators.
Police are also monitoring about 150 protesters who are marching north on Western Avenue into Hollywood.
So far only one arrest has been made.
The LAPD called a citywide tactical alert after demonstrators protesting the not guilty verdict in the George Zimmerman case blocked traffic on the 10 Freeway in the Mid-City area Sunday evening.
The California Highway Patrol said "police activity" around the 10 Freeway and Crenshaw Boulevard has jammed traffic. Motorists are urged to avoid the area.
No arrests have been made, and no one was hurt. LAPD sources said a splinter group of a larger protest walked down an on-ramp to the 10 Freeway and stood mostly in the eastbound lanes.
Officials said portions of the 10 were closed from 6:20 p.m. to 6:44 p.m. but have since reopened.
Photos and videos showed both sides of the 10 Freeway blocked and demonstrators milling about the freeway.
As tourists looked on, the protesters chanted: "What do we want?" "Justice!" "When do we want it?" "Now!" The demonstration was one of many in major U.S. cities Sunday after neighborhood watch volunteer George Zimmerman was acquitted Saturday night in the 2012 death of Trayvon Martin in Florida.