Officers and firefighters responded shortly after 1:30 p.m. to the incident in the 23500 block of Anza Avenue, according to the Torrance Police Department.
Two of the injured were transported to a hospital as a precaution, a police spokesperson said. Their conditions were not immediately known.
Two apartment units at the scene were damaged in the blast and windows and doors could be seen with heavy damage, along with shattered glass on the sidewalk.
"We just heard a really really loud noise," said one woman who lives nearby. "It seriously sounded like a refrigerator falling or something."
Anza Avenue was closed in both directions at the scene as an investigation continued. The public was urged to avoid the area.