BILOXI, Miss. -- A freight train smashed into a charter bus in a coastal Mississippi city on Tuesday, pushing the bus 300 feet down the tracks and leaving at least four people dead, authorities said. Rescuers spent more than an hour removing passengers, cutting through the bus’ heavily damaged frame to extract the last two.

CBS affiliate WLOX-TV reports that dozens of other senior citizens from Texas were injured when the bus got stuck on the tracks in Biloxi.

Police Chief John Miller, however, said it was unclear why the bus had stopped.

The bus was apparently stopped on the tracks when the 52-car train, pulled by three locomotives, slammed into it, Miller said.

“We’re not sure why,” Miller said. “We don’t know if there were mechanical issues or what was taking place.”

City spokesman Vincent Creel said the train hit the bus at a crossing in downtown Biloxi just before 2:15p.m.

Officials said there were four confirmed fatalities resulting from the crash. The passengers on the bus were senior citizens traveling from Austin, Texas, to the casino in Biloxi, WLOX-TV reports.

“It’s a terrible tragedy,” Miller said. “I know there’s a lot of families that are going to be impacted here.”

Crews were seen removing people through the emergency windows and “jaws of life” were needed to extricate two victims. All other passengers were removed from the bus within 30 minutes, Miller said.

Michelle Crowley of the Biloxi fire department said 40 people were injured. Of those, seven were in critical condition.

The names of the dead have not been released.

A woman who lives about a block from where the train and bus finally came to a stop after the train crashed into the bus says she heard a “loud boom” and knew immediately what had happened.

Cecelia McDonald said she ran out of her house and saw a scene of carnage.

A spokesman for CSX told The Associated Press the freight train was headed from New Orleans to Mobile, Alabama, at the time of the deadly crash. Gary Sease said the train had three locomotives and 52 cars. The train crew was not injured.

Federal Railroad Administration spokesman Marc Willis said the agency is sending three inspectors to investigate, while Mississippi is sending one. The National Transportation Safety Board said it is also investigating.