Two cars - a Vauxhall Tigra and a BMW - collided on the westbound carriageway between junctions 19 and 20, near Milnrow.
The accident blocked the carriageway for several hours.
The 65-year-old driver of the Tigra was treated at the scene for serious injuries and was later taken to Rochdale Infirmary.
The other driver was uninjured.
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