The exact cause of the explosion has not yet been released. Officials say that the explosion appears to be related to an underground vault explosion.
Click here for a slideshow from the scene of the explosion, or mouse over the Eyewitness News Story Window above to watch video for this story.
Air ambulances were immediately sent to the scene. Two firefighters and one civilian were injured in the explosion. The civilian reportedly received minor injuries. One firefighter, Brent Lovrien, died from injuries sustained in that explosion. The second firefighter, Engineer Anthony Guzman, was in surgery Wednesday evening at UCLA Medical Center, with injuries including a broken ankle and a compound fracture in his arm. Guzman is reportedly out of surgery in stable condition. The firefighters were part of L.A. City Fire Station No. 95, according to the authorities.
Authorities say that at approximately 2:20 p.m. firefighters responded to an explosion at the 8800 block of Sepulveda Blvd. at the corner of Manchester Ave. and La Tijera Blvd. near LAX. Arriving on the scene, firefighters saw smoke coming from a number of manholes and from a building.
The explosions ripped through the stucco walls on a corner of the two-story building, which houses the Water and Power Community Credit Union.
When firefighters entered the rear of the building, a second explosion occurred, Fire Department Deputy Chief Mario Rueda said during a news conference.
"It appeared to be at least electrical in nature because of the substations that are underneath Sepulveda, but we don't have a cause of the explosion at this point," Rueda said.
"I don't have a theory on how it occurred. I can tell you smoke is combustible and can be explosive when it reaches the right temperature, and with a source of ignition, smoke can be explosive," he added.
Mayor Antonio Villaraigosa and L.A. City Fire Dept. Chief Douglas Barry spoke at a press conference Wednesday evening at Centinela Freeman Regional Medical Center, where the first firefighter succumbed to his injuries at about 5 p.m.
Brent A. Lovrien was 35 years old. He was a 10-year veteran of the LAFD, assigned at Fire Station 95 since October 2005, according to the L.A. City Fire Dept.
Engineer Anthony J. Guzman is 48 years old. He is an 18-year veteran of the LAFD, assigned to Fire Station 95 since February 2002, according to the L.A. City Fire Dept. He received multiple bone fractures and facial trauma in Wednesday's incident.
Numerous entities will be investigating the cause of the explosion and the surrounding events, including the L.A. City Fire Dept. and L.A.'s Coroner's Office, according to Chief Barry.
According to Chief Barry, psychologists will be assisting members of the Fire Dept. to help them deal with any emotional trauma as a result of the fatal incident.
Elsa Ramon contributed to this report.
Click here for a slideshow from the scene of the explosion.