FBI agents are probing the background and possible motivation of a man who opened fire at a packed terminal at Los Angeles International Airport and shot dead an unarmed federal agent.

Authorities have identified the suspected shooter in Friday's attack as Paul Anthony Ciancia, 23, and said he was shot and wounded by police in an exchange of gunfire at the airport's Terminal 3.

Late on Friday, FBI agents armed with a search warrant combed through Ciancia's home in the Los Angeles area, FBI spokeswoman Laura Eimiller said.

The shooter was armed with an assault rifle and touched off panic and chaos at one of the world's busiest airports. Hundreds of travellers ran frantically for safety or dove for cover behind luggage, as loud alarms blared.

The gunman, a US citizen who appeared to be acting alone, pushed through the screening gates and ran into an area where passengers board flights, before law enforcement officers caught up with him in a food court, Patrick Gannon, chief of the Los Angeles Airport Police, said at a news conference.

The officers shot him at least once and took him into custody, he said.

At least two Transportation Security Administration (TSA) employees were shot, one fatally, said Special Agent David Bowdich of the FBI. The slain TSA agent, identified as 39-year-old Gerardo Hernandez, was the first from the agency, tasked with screening air passengers, to die in the line of duty.

Paramedics took five people wounded at the scene of the shooting to area hospitals, officials said.

Family concerned

The investigation into the attack will probe the shooting itself as well as the gunman's background and possible motivations, Bowdich said on Friday.

"Our goal is to do a true scrub on the individual to find out what was the tipping point for this person," he said.

In New Jersey, police and FBI agents descended on Ciancia's family's home in Pennsville Township. Local police chief Allen Cummings said he had been contacted by Ciancia's father before the shooting, after a worrisome text message from the young man to his brother.

The police chief declined to elaborate on the nature of the text message but said that family members told investigators they had no previous indications that Ciancia, who moved to California about 18 months ago, was troubled.

Tom Ridge, former secretary of the US Department of Homeland Security which oversees the TSA, said he did not think security changes at airports could help prevent such an incident from happening again.

Ridge said in a phone interview he opposes the idea of arming TSA agents.

"That [arming them] requires a level of sophistication and law enforcement training, and at the end of the day, I'm not sure it's going to make that much of a difference," he said.

The incident affected an estimated 1,550 arriving and departing flights carrying more than 167,000 passengers, airport spokeswoman Nancy Castles said in a statement.

A number of those flights were grounded or diverted as police evacuated passengers and shut down three terminals during the incident.

Source: Reuters