A freight train has crashed into a bus full of Texas tourists visiting Gulf Coast casinos, killing four in Biloxi, Mississippi.
Forty people were hurt, seven critically. The cause of the Tuesday afternoon crash remains under investigation.
Witnesses told Mississippi news outlets the bus appeared to have been stuck on the tracks when it was hit.
The crossing is on a steep embankment and has a sign warning drivers that it has a low ground clearance.
Authorities on the scene said it took more than an hour to get everyone aboard the bus out of the wreckage. Two people had to be removed with metal-cutting equipment.
The CSX Transportation locomotive pushed the bus about 300 feet before coming to a stop with the mangled bus still straddling the tracks.
Jim DeLaCruz, a passenger who was in the back of the bus with his wife, told The Sun Herald that they were trying to get off.
"The bus tried to clear the tracks and got stuck right in the middle and it couldn't budge, and the train just kept coming and kept coming," he said.
Police chief John Miller said he was unsure why the train was stopped on the tracks.
"We don't know if there were mechanical issues or what was taking place," he said.
Mr Miller said the Echo Transportation bus had come from Austin, Texas, carrying passengers to one of Biloxi's eight casinos.
Ameet Patel, senior vice president of regional operations for Penn National Gaming, owner of Hollywood Gulf Coast Casino in Bay St Louis and Boomtown Biloxi Casino, said the bus was travelling from the Hollywood casino to the Boomtown casino at the time of the crash.
The weeklong trip was organised by a senior citizens' centre in Bastrop, Texas, about 30 miles east of Austin. Some passengers boarded in each city.
They also were supposed to visit New Orleans and then return home on Saturday, according to a flier about the tour posted by Texas media.
The names of the dead were not immediately released.
Michelle Crowley of the Biloxi fire department said 40 people were injured; of those, seven were in critical condition.
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.
Witnesses told The Sun Herald of Biloxi that the bus was stuck on the tracks for about five minutes before the train hit.
Some people were getting off the bus as the driver tried to move it, and at least one person was shoved under the bus when the train hit, said Mark Robinson, a Biloxi native.
In addition the sign warning of a low ground clearance, the crossing has a bell, lights and crossing arms.
Biloxi Fire Chief Joe Boney says rescuers needed one hour and four minutes to clear everyone from the wreckage. Two people had to be cut out of the bus.
Vincent Creel, the city spokesman, said 48 passengers and the driver were on the bus.
The train was headed from New Orleans to Mobile, Alabama, at the time of the crash, said CSX spokesman Gary Sease. He said the train crew was not injured.
The single track is the CSX mainline along the Gulf Coast, passing through densely populated areas of southern Mississippi.