The car involved failed to stop at a Garda checkpoint.
At around 11.30PM last night a car drove the wrong way onto the carriageway and collided with a lorry.
The three causalities were occupants of the car, which burst into flames following the impact.
The driver of the lorry was brought to Tallaght hospital for treatment.
Gardai say the car had failed to stop for them earlier in the evening but was not being pursued at the time of the crash.
The incident has been referred to the Garda Ombudsman.
Forensic Collision investigators are currently at the scene.
The N7 inbound is expected to remain closed and diversions have been set up through Saggart.
