An Amtrak train carrying more than 200 passengers crashed into a dump truck in rural Missouri on Monday, killing three people and injuring an unknown number, the authorities said. It was the second fatal accident involving the railroad service in two days.

Two of the people killed were on the train, and the other was in the truck, the authorities said. The extent of the passengers’ injuries was not immediately clear.

The train was traveling from Los Angeles to Chicago when it hit the truck, which was obstructing a public crossing at 12:42 p.m. near Mendon, Mo., about 100 miles northeast of Kansas City, Mo., Amtrak said.

Eight cars and two locomotives derailed, Amtrak said, and most of the cars ended up on their sides.

Lt. Eric F. Brown of the Missouri State Highway Patrol said at a news conference on Monday that the crash had occurred at a crossing on a gravel road “with no lights.”

The Missouri State Highway Patrol said it had responded along with other agencies. Amtrak said it also had deployed its own emergency personnel to the scene to help passengers, employees and their families. It said further details would be provided “as available.”

Gov. Mike Parson of Missouri told reporters that it was a “terrible situation.”

Photos posted on Twitter by a man who said he was on the train showed passengers standing atop overturned Amtrak cars, helping each other out, as others walked along the railroad tracks. Another photo showed four large rubber tires on an axle lying near the tracks.

Later, the man posted a photo showing that passengers had gathered in a high school gymnasium near the scene of the crash.

“So thankful for the people here, safely at the Northwestern high school near Mendon,” he wrote. “This town pulled together to help everyone.”

The crash came one day after another Amtrak passenger train crashed into a four-door sedan at a crossing without a train signal or guardrails in a rural area of the East Bay in Northern California on Sunday, killing three people and critically injuring two others including a child, a spokesman for the local Fire Department and emergency services said.

The victims in that crash were pronounced dead at the scene, according to Steve Aubert, a fire marshal with the East Contra Costa Fire Protection District. That five-car train was carrying nearly 90 people, a spokeswoman for Amtrak said in an email.