Two people - believed to be an adult and child - have died after being hit by a train during the evening rush hour.
London Fire Brigade said it was called to reports that an adult and child had fallen on to the tracks at Ealing Broadway, in west London, shortly after 6pm.
British Transport Police (BTP) said the deaths were being treated as "unexplained" and it was still to early to confirm the identities of the victims.
A BTP spokesman said: "We were called at 6.10pm to Ealing Broadway station following reports that someone had been hit by a train.
"We attended along with the Metropolitan Police, London Ambulance Service and London Fire Brigade and discovered two people had been struck and killed by the train.
"We're still working to determine the identities of the deceased or how they come to actually be on the tracks.
"At present we're treating the incident as unexplained."
Police have appealed for witnesses or anyone with information to come forward.
Following the incident, Heathrow Express said all services between Paddington station and Heathrow airport had been suspended, while First Great Western said there were delays of up to 90 mins to and from Paddington.
London Ambulance Service said staff including its hazardous area response team had been sent to the station but that two people had been pronounced dead at the scene.