A 15-year-old boy and a 72-year-old man were killed when a train collided with a car in Horsham, West Sussex.
Officers were called at 8.47am on Saturday to Barns Green level crossing in Horsham following reports of a collision, the British Transport Police (BTP) said.
The pair, who are members of the same family, died after a train struck their car at 8.40am, the force said. Their family is being supported by family liaison officers.
DI Brett Walker, from BTP, said: “This is an extremely tragic incident and our thoughts are with the family at this difficult time.
“Our officers have been working at the scene, and will continue to do so for the rest of the day, to ensure we gain as much information about how the collision happened. People should expect some disruption to services in the area while we investigate. I would like to thank the community in Barns Green for their support and patience.
“Local people will see more of our officers in the area throughout the day and I would urge anyone who saw what happened, or feels they may have any information which would be relevant to our investigation, to contact us.”
The BTP said the Rail Accident Investigation Branch had been notified.