A passenger train traveling from Los Angeles to Chicago derailed in Missouri on Monday after hitting a dump truck that was blocking a public crossing, Amtrak said.

Some people aboard were injured, but it was not immediately clear how many, according to Amtrak and local officials.

The Southwest Chief was carrying about 243 passengers and 12 crew members when the collision happened near Mendon at 1:42 p.m., Amtrak said. Eight cars and two locomotives derailed.

Helicopter video shown by KMBC-TV in Kansas City from the scene showed rail cars on their side as emergency responders used ladders to climb into one of them. The video also showed six medical helicopters parked nearby waiting to transport patients.

Three passengers were taken to University Hospital in Columbia, hospital spokesman Eric Maze said. He did not have information on their conditions.

Passengers on the train included high school students from Pleasant Ridge High School in Easton, Kansas, who were headed to a Future Business Leaders of America conference in Chicago, Superintendent Tim Beying told The Kansas City Star.

The Southwest Chief takes about two days to travel from Los Angeles to Chicago. Mendon, with a population of about 160, is about 84 miles (135 kilometers) northeast of Kansas City.