Emergency services responded to a serious incident near junction five (Tunstall Road), where the anticlockwise lanes were closed.
Highways England had warned at 8.30am that the closure could remain in place for a number of hours but said a short time later that it could reopen sooner than anticipated.
The agency tweeted: "Super fast work by @WYP_RPU and our #TrafficOfficers mean we are in the process of removing the closure of the #M621 at J5. Traffic currently held for us to collect our kit. Will update once all clear."
The road was fully reopened at around 8.40am, although it took some time for tailbacks on the M621, M1 and M62 to clear.