The Transportation Security Administration said a number of its employees were injured, one fatally.
A lone suspect – whom law enforcement officials named to US media as 23-year-old Paul Ciancia – was wounded by police and detained.
Flights in and out of the busy airport were temporarily halted.
LA Airport police chief Patrick Gannon told reporters a “lone shooter” came into Terminal 3 at 9:20 local time.
The suspect “pulled an assault rifle out of a bag and began to open fire in the terminal”, he said.
Paul Ciancia then proceeded to a security screening area and continued shooting.
Witness Brian Keech told the Associated Press news agency he had heard “about a dozen gunshots” from inside the security gate at Terminal 3.
Authorities actively engaged the shooter, during which time the suspect was wounded and later arrested, Patrick Gannon added.
The Transportation Security Administration later issued a statement reporting “multiple Transportation Security Officers were shot, one fatally”.
A local hospital official told reporters one of the injured was listed in critical condition, while two other victims were listed in fair condition.
The Federal Aviation Administration (FAA) barred all flights landing at the airport during the incident, and outbound flights were delayed.
LA Mayor Eric Garcetti said those inside the airport were now safe and outbound flights would resume in areas other than Terminal 3.
Inbound flights were currently arriving at half the normal rate, officials said.
President Barack Obama expressed concern about the shooting, but said he would leave law enforcement to talk about it.
Witness Brian Adamick told the Los Angeles Times he and several other passengers went through a Terminal 3 emergency exit and on to the tarmac during the incident.
“While I was on the tarmac, I heard two gunshots from the same area where the people had been running and screaming,” Brian Adamick told the newspaper.
qbr4wRJxtQo RT9XpHF7-soImage source: Wikimedia Commons President-elect Donald Trump celebrated his election victory at the Ultimate Fighting…
Millions of voters across the US chose to return Donald Trump to the White House…
Donald Trump declares victory in the US election as he addresses jubilant supporters in Florida.…
Stocks around the world are rising as Donald Trump appears to be on the cusp…
Donald Trump has won Pennsylvania, North Carolina and Georgia and taken a lead over Kamala…
Quincy Jones, the celebrated musician and producer who worked with Michael Jackson, Frank Sinatra, Ray…