Los Angeles County firefighters responded to the five-vehicle crash shortly after 3 a.m. on the eastbound 60 Freeway at the 57 Freeway.
One person was pronounced dead at the scene. Several others, including two children, were transported to Pomona Valley Hospital Medical Center.
The exact number of victims and their conditions were not immediately clear.
The eastbound lanes of the 60 Freeway at the 57 transition road were closed for several hours overnight, as crews worked to clear the scene. All lanes opened at about 7 a.m.
The cause of the crash was under investigation.