A cache of roughly 50 pounds of old, deteriorating dynamite was found in a warehouse following a standoff, and authorities burned down the storage unit containing the explosives after determining they were too dangerous to move.

Television coverage showed bright orange flames and a thick plume of smoke erupting through the building's roof shortly before 6:30 a.m., and the storage unit was fully engulfed minutes later.

"It's so unstable ... it's best to burn it in place," said Los Angeles Police Lt. Paul Vernon.

Flames spread to adjacent units, but firefighters managed to contain the blaze and keep it from burning the entire warehouse.

Police believe the location was being used to house stolen goods and that the dynamite was not connected to terrorism, Vernon said.

About 150 firefighters were at the scene and approximately 50 people were evacuated from the surrounding area, Fire Department Captain Lou Routoli said.

The California Highway Patrol, at the request of the LAPD, closed a section of Interstate 405 while the dynamite was burned during the morning rush hour. The freeway is one of the main links between Los Angeles and cities to the north, and it reopened after about 45 minutes.

Commuter trains from Ventura to Los Angeles were not running during the operations, Metrolink officials said.

The incident began Tuesday night when police responded to a call from a man who found a package in his apartment freezer that contained a stick of dynamite, police said. He told officers it belonged to his former roommate. Police traced the dynamite to the warehouse, where officers found two men, said LAPD Officer Mike Lopez.

A man in his 20s was immediately arrested but a man in his 40s ran inside the building, prompting a six-hour standoff that ended with his surrender Tuesday night, Lopez said.

Officers found the dynamite during a search of the building and also found what police suspect are stolen goods, he said.

Three people were arrested for investigation of possessing explosives and one for investigation of possessing a stolen car, Vernon said.

He said police do not know how the suspects got the dynamite.