SAN DIEGO -- The third brush fire to erupt on the grounds of Camp Pendleton in less than 24 hours blackened scores of open acres and forced the complete closure of nearby Interstate 5 for several hours Tuesday.

A landscaper cutting weeds on the east side of the freeway near Las Pulgas Road sparked the non-injury blaze shortly before 10:30 a.m., according to Marine Corps officials and the California Highway Patrol.

As the flames spread rapidly to the west, the CHP shut down a stretch of I-5 between Harbor Drive in Oceanside and Cristianitos Road at the Orange County border.

Motorists were diverted onto surface streets and, at times, directed to turn around through center medians.

North County Transit District also shut down a stretch of train tracks that runs alongside the freeway, delaying several Amtrak runs between Oceanside and San Juan Capistrano by about 90 minutes, NCTD spokesman Tom Kelleher said.

Ground and airborne personnel had the roughly 110-acre fire under control by early afternoon, but the freeway remained closed in the area while crews doused hot spots, authorities reported.

Shortly after 12:30 p.m., officers got the go-ahead to reopen both sides of the interstate, CHP public information Officer Ray Scheidnes said.

On Monday afternoon, several fires erupted in the southeast reaches of Camp Pendleton, prompting the evacuation of thousands of area residents. By Tuesday morning, the flames had scorched about 3,000 acres but had caused no reported structural damage or injuries.