A 49 year old man has died and another two have been taken to hospital with serious injuries.
Officers have established that a black Audi A3 had been travelling on the carriageway when it was involved in a crash with the central reservation before coming to a stop in the middle lane.
An unknown car drove past a short time later and pulled up on the hard shoulder, surveyed the scene, then drove off.
Minutes later the Audi was involved in a further collision with a Ford Focus and a VW Caddy van.
Officers are now urging the driver of the unknown car that drove past the initial incident to come forward and assist with enquiries.
There is no suggestion of any wrongdoing by this person.
We have been carrying out numerous enquiries since the tragic events of this morning and now have further information. I want to make it clear that this person is not in trouble but they may hold key information that may assist the investigation.
The anti-clockwise carriageway between J18 and J19 is expected to be closed until midday so motorists are advised to avoid the area.
Anyone with information should contact GMP’s Serious Collision Investigation Unit on 0161 856 4741 or the independent charity Crimestoppers, anonymously, on 0800 555 111.