SAN DIEGO -- Amtrak and Coaster riders experienced 20- to 30-minute delays through the morning and afternoon Tuesday in the aftermath of a late-night freight-train derailment in Sorrento Valley.

The non-injury rail accident occurred shortly before 10:30 p.m. Monday in a canyon just north of Miramar Road, according to North County Transit District. About a half-dozen empty boxcars derailed, and several toppled onto their sides.

Coaster customers were taken by bus between depots in Sorrento Valley and downtown San Diego, according to the NCTD, which operates the commuter-train service.

Amtrak passengers, likewise, were driven in both directions between San Diego and Oceanside through the morning and early afternoon, said Vernae Graham, a spokeswoman for the government-owned national rail line.

Crews had the tracks cleared by shortly before noon and then began working to repair a roughly 300-foot section of railway, according to NCTD spokeswoman Sarah Benson.

"The damage was pretty minimal, actually," she said, adding that workers were replacing a number of ties.

Amtrak resumed its service through the area about 2:30 p.m., completing a southbound Pacific Surfliner run that originated in San Luis Obispo, Graham said.

Coaster service restarted about a half-hour later, initially running roughly 25 minutes behind schedule, according to Benson. Decreasing delays were expected to continue into the late afternoon or evening, she said.

"It just kind of takes us a little time to get the trains back out there, lined up and going where they need to go," Benson said.

The first northbound Amtrak run of the day left downtown San Diego at 4 p.m. As the train approached the site of the accident, it slowed and stopped several times, and an employee made an announcement alerting passengers that they would be able to see several of the damaged cars alongside the tracks.

The train then very slowly passed three boxcars, one on its side, another -- the most obviously damaged one, with its metal sides dented and torn -- leaning to one side, and a third upright.

The freight carriers were on an embankment near a roughly 150-foot bluff above a ravine on the east side of the rails.

The cause of the derailment of the BNSF cargo train was under investigation.