One of the suspects came to the shipping yard at Farragut and Anaheim streets just before 10:30 p.m. Sunday. He pretended to be lost and lured the guard from his post.
The suspects assaulted the security guard, a driver and an employee of the yard and tied them up in an office. They then loaded five containers onto trailers they brought with them for the heist and took off.
"They were looking for something specific, so they obviously knew that something was in the containers that they were looking for," said Los Angeles Police Department Harbor Division Sgt. Jeff Hamilton. Authorities did not say what the stolen items were.
Investigators said the suspects told the assault victims they had a gun, but a weapon was never seen.
The guard, driver and employee were able to untie themselves and call police. They were transported to an area hospital where they were treated for non life-threatening injuries.
Police are searching for witnesses who may have seen the crime happen. They will also comb surveillance footage that may lead them to the suspects.
Investigators only had vague descriptions of the suspects and the trailers. They said one of the trailers was white with the letter "L" on the door.
Anyone with information about the crime is asked to contact the LAPD Harbor Station at (213) 485-2507.
City News Service contributed to this report.