Hundreds had gathered in the southern part of the city outside Hussle's The Marathon Clothing store where the Grammy-nominated musician was gunned down on Sunday in a suspected gang-linked attack that wounded two other people.
A stampede started just past 8:00 pm (0300 GMT Tuesday) during the service, but it was not clear what triggered it.
"Reports of shots fired at the vigil do not appear to be accurate. We do have injured in the chaos and are attempting to restore order," the Los Angeles Police Department said on Twitter.
The Los Angeles Fire Department said in a statement that it transported 19 patients, two of them critical, and another two with serious injuries. The rest had "non-life threatening injuries."
It added that there was "no evidence of any gun shot wounds" and that most people sustained "trample injuries."