“We’re working now to finish the accident and investigation”
The train, which had been travelling from Ronkonkoma to New York City, hit the vehicle as it was approaching Westbury station at about 7pm on Tuesday (12am Wednesday GMT).
A spokesman for the rail service said the collision happened at a crossing in School Street.
Three people in the truck were killed after the driver tried to beat the crossing, but became trapped when the guards on either side lowered.
After smashing into the vehicle, the train – carrying about 200 people – derailed and crashed into the platform.
As the car spun around it was hit again by a westbound train carrying 100 people.
Philip Eng, President of Long Island Rail Road, said: “There were three fatalities – all from the vehicle.
“We had seven passengers that were taken to hospital just as a precautionary measures.
“An engineer and a conductor were also taken to hospital for injuries.
“And we’re working now to finish the accident and investigation.
“My understanding is that the gates were down and the lights were flashing.”
The victims could not be identified immediately as the bodies were badly burned.
Authorities said about 900 people were safely evacuated from the station and both trains.
New York Governor Andrew Cuomo has since called for a “full investigation into the collision”.