At least 20 passengers suffered minor to moderate injuries, authorities said.
The crash occurred when the driver of the big rig carrying cotton trash failed to yield and hit the train, authorities said. The impact pushed the two passenger cars and the locomotive off the tracks south of Hanford, a farming town.
The train traveled about 600 feet after the collision before hitting a switchback and derailing, according to California Patrol Officer Scott Harris.
The crash occurred at a crossing that was equipped with control gates, Putnam said.
After the crash, metal pieces from the truck could be seen inside the train, which was covered by cotton seeds. Several pieces of luggage were also scattered about.
The injuries to passengers were described as bumps, bruises, scrapes and possibly broken bones by Kings County Assistant Sheriff Dave Putnam.
Eight of the injured passengers were taken to Adventist Medical Center in Hanford and five more were enroute, said hospital spokeswoman Christine Pickering. She did not provide details on the extent of their injuries.
"We did call in additional physicians and staff," Pickering said.
Four additional injured passengers were taken to nearby Adventist Medical Center in Selma.
The train was on its way from Oakland to Bakersfield, according to Amtrak. It had four rail cars and a locomotive.
The truck driver suffered minor injuries, according to California Highway Patrol spokesman Jerry Pierce. The CHP will investigate the crash.
"This is a big, huge chaotic scene with lots of agencies involved," Pierce said.
Pierce said the other passengers have been taken to an auditorium in Hanford, where they will board a train and continue to their destinations or family members will pick them up.