At least four or five shots were heard about 4:15 p.m. near Vermont Avenue and Exposition Boulevard, said Officer Mike Lopez of the Los Angeles Police Department.
One man was struck by gunfire and taken to a hospital in serious condition, Lopez said. The man later died of his injuries, and his identity was not released pending notification of his family.
It's unclear what led to the gunfire.
Police had detained an 18-year-old man for questioning in connection with the shooting, and he was later identified as the suspect, Lopez said. As of 11 p.m., he was in the process of being booked and his identity was not available.
The shooting occurred at Jesse A. Brewer Jr. Park, just a few yards from the Natural History Museum of Los Angeles County and the California Science Center.
USC issued an alert at about 5 p.m. asking students, faculty and staff to avoid the park.
"LAPD investigation at Jesse Brewer Park at the [southeast] corner of Expo and Vermont continues, however there is no threat to USC," the alert said.
The park was named in 1998 for Brewer, an African American LAPD officer who broke through racial barriers in the department during his nearly 40-year career.
This story will be updated as more information becomes available.