The Garda watchdog, GSOC is also investigating the collision, which happened at the Northumberland Road and Haddington Road junction at 10:45pm last night.
Among the six injured on the bus, two men are in a serious condition in St Vincent's Hospital.
The scene has been preserved and road is closed with diversions in place.
Gardai are appealing for witnesses and any motorist who may have camera footage to contact them.
Investigations are ongoing and further updates will follow.
Firefighter/Paramedics are at the scene of a serious incident on the @M50Dublin Northbound junction 7 Blanchardstown.
The road is CLOSED Northbound. Southbound users please pay attention to the road in front of you to avoid collisions.
Avoid the area. @aaroadwatch pic.twitter.com/eie4w61TpM— Dublin Fire Brigade (@DubFireBrigade) October 3, 2020
