Passengers on board the train recounted a jolt, a big brown dust cloud and rail cars tipping over like dominos - all of it happening within seconds.
WATCH: Boy Scouts jump into action after deadly Amtrak derailment
Video shows aftermath of Amtrak train derailment in Missouri
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Jason Drinkard was about two hours into his trip when the train derailed. Drinkard and his wife were chaperoning six high school students to the Future Business Leaders of America Conference in Chicago.
"It looked like a bomb had gone off because bags and seat cushions were everywhere, people were bleeding, people were injured," Drinkard said. "You could hear the metal twisting and crunching. You could hear the rush of it dragging across the gravel."
Drinkard said they had to stand on the luggage racks and climb up on the seats to make their way out.
"I remember when we got off the train and looking at the track, it was completely pulled up, it was twisted," he said.
After realizing his whole group was okay, Drinkard immediately helped others.
"For whatever reason, I brought my tiny first aid kit and brought it with me, just in case," Drinkard said. "There was a wide array of injuries. There were a lot of people who were cut and bleeding."
The other fatalities were train passengers. There were 275 passengers on the train with 12 board crew members. The National Transportation Safety Board arrived on scene today to investigate. The Missouri crash is the second fatal Amtrak crash in two days.
Drinkard said he is thankful he and his group survived with a few bumps and bruises. While some of the students were hoping to continue their trip to Chicago for the FBLA conference, Drinkard thought it would be best to return to their relieved families in Olathe, Kansas.
WATCH: Missouri State Highway Patrol update on Amtrak derailment
Missouri State Highway Patrol give update on deadly Amtrak derailment
Police said they first got calls about the Southwest Chief train, traveling from Los Angeles to Chicago with stops in between, striking the truck at about 12:43 p.m. in a rural area southwest of Mendon.
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First responders arrived just after 1 p.m., police said. The incident happened at an "uncontrolled crossing" on a gravel road with no lights or electronic controls, according to law enforcement.
Amtrak officials said the truck was obstructing a public crossing, though police did not say if the truck was stuck on the tracks. As a result of the impact, seven of the train's eight cars derailed, police said.
Two of the people killed were on the train, while the third was in the dump truck, police said. They have not yet been identified.
"There was dust and dirt everywhere. I was on the side of the train that hit the ground first, so everyone fell on top of us," said Loralai Kruid, a student on the train.
Sixteen Boy Scouts from Wisconsin, who were traveling on the train, also jumped into action, helping administer first aid to victims.
Boy Scouts jump into action after Missouri Amtrak train derailment
"One scout wrapped his hand, took his shirt off to break windows to get people out," Troop 73 Scoutmaster Dan Skrypczak said. "Another scout went and comforted the driver of the truck that was hit to stabilize him. They were tandem working on the gentleman when he expired, so that scout is pretty shook up."
Hedrick Medical Center said they have accepted four patients. They did not offer information on those patients' conditions.
University Hospital in Columbia, Missouri confirmed they received three patients from the derailment, but did not offer any further details.
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Video shows a desperate scene, with several derailed train cars on their sides. Passengers sat or stood atop those cars after apparently climbing out of windows.
"Local authorities are currently assisting customers and we have deployed Amtrak resources to assist. Additional details will be provided as available," the company said in a statement.
The train was scheduled to arrive at Union Station about 6 p.m., and it's unclear how many passengers aboard had Chicago as their final destination.
Mendon is in Chariton County, about 100 miles northeast of Kansas City.
Amtrak said anyone with questions about friends and family aboard the train should call 800-523-9101.
The National Transportation Safety Board arrived at the crash site Tuesday morning. The agency is seeking the train's event record and other information, including how fast it was traveling. The speed limit in the area is 90 mph, the NTSB said in a press conference Tuesday afternoon.
The NTSB called for safety upgrades at railroad crossings nationwide after people in that rural community said they've been asking for this crossing to be addressed for years.
This comes one day after an Amtrak train collided with a car in California, killing three people.
ABC News contributed to this report