The two-vehicle crash happened at around 5.30am on Sunday on the southbound carriageway between Junction 11 at Tallaght and Junction 12 at Firhouse.
Emergency services attended the scene, with those injured subsequently transported to hospital for medical treatment. Gardaí are also at the location as investigations into the collision continue.
The M50 southbound section between Junction 11 and Junction 12 has been closed while emergency services deal with the incident.
Motorists are being advised to avoid the affected stretch of road where possible and to allow extra time for their journeys, with delays expected in the area. Diversions are in place.
