Smoke, Flames Sever Traffic on I-5 Freeway : Brush fire: Rush hour between Orange and San Diego counties is a nightmare. Roadway is later reopened as blaze continues to burn.

A brush fire fanned by Santa Ana winds blackened 7,000 acres in and around Camp Pendleton on Wednesday, severing traffic at the Orange County-San Diego County line on Interstate 5, delaying motorists for up to five hours, jamming surface streets and swaddling the San Onofre area in billowing plumes of smoke that were visible for more than 30 miles.

Passenger train service also was intermittently halted until midday, a nuclear power plant alert was triggered and up to 300 residents were temporarily evacuated from a trailer park, authorities said.

With the afternoon rush hour at hand, the California Highway Patrol reopened a 20-mile stretch of freeway that had been closed for 12 hours and began escorting groups of 300 drivers through the smoke-filled, soot-coated stretch. The freeway was fully open by shortly after 5 p.m.

Camp Pendleton officials said they do not expect the fire, which had burned 7,000 acres as of Wednesday afternoon, to be controlled until today. A few buildings at the U.S. Border Patrol checkpoint were singed, but no one was injured. No cause has yet been determined.

The fire, which began Tuesday night, forced the CHP to close Interstate 5 near the San Diego County-Orange County border Wednesday morning, causing a six-mile back-up. Motorists were forced to travel around the fire by way of Interstates 91 and 15 and the 55 Freeway.

While frustrated motorists fumed, passenger rail service linking San Diego and Los Angeles was intermittent until the railroad was reopened at 1 p.m.

“It’s been like the perils of Pauline here,” said Cliff Black, an Amtrak spokesman in Washington.

Only two trains--one northbound and one southbound--made it across the base early in the day, forcing would-be passengers to endure delays of up to eight hours, Black said. Train depots in Oceanside and San Juan Capistrano became way stations for marooned rail passengers.

Wednesday afternoon, bright lines of fire were visible on ridge tops and giant clouds of white, gray and amber smoke poured out of canyons. A six-mile stretch on both sides of I-5 from the San Onofre nuclear power plant to the Las Pulgas Road exit was ravaged where flames had jumped across the lanes, burning the center divider and consuming dry scrub brush all the way to the ocean.

Staff writers John M. Glionna and Sonni Efron and correspondents Wendy Paulson and Len Hall contributed to this story.