The incident occurred about 1 a.m. near Hubbard Street, the Los Angeles Police Department said.
All eastbound lanes and onramps between the 5 Freeway and Hubbard Street were expected to be closed until at least 8 a.m., according to the California Highway Patrol. Drivers can get on the freeway at Maclay Street, said CHP officer Cheyenne Quesada.
The LAPD said the incident will likely lead to a homicide investigation.
According to witnesses, a red car was being driven erratically when a woman came out of the car and was hit by at least two other vehicles before her body came to a rest in the fast lane, NBC-LA reported.
LAPD Lt. Paul Vernon told KTLA that another driver saw the car weaving across all lanes and onto the median before it returned to the freeway. That's when the passenger door popped open and the woman exited the car.
Vernon said evidence shows she was alive at that time and was hit moments later, he said.
The first car that hit her stopped, but others ran over the body, police told NBC.
"They probably never knew they were running over a body," Vernon said.
Witnesses walked onto the freeway and directed traffic around the body until emergency vehicles arrived, according to CHP logs.
"The question of the day is, why did she come out of the car? Under her own power? Was she pushed?" Vernon said.