The motorway was closed from 4am to 8am after a crash between junctions 33 (Galgate, Lancaster South, A6) and 34 (Heysham, Morecambe).
North West Ambulance Service said one casualty has been taken to hospital in a serious condition. You can read our report on the casualty here.
National Highways said there was around 6 miles of congestion northbound after the motorway reopened.
Earlier this morning, a Highways spokesman said: "Please be aware that this earlier M6 northbound incident between J33 to J34 is causing delays of 30 minutes above normal journey time for this time of day.
"There is approximately 6 miles of congestion on approach. Please allow time for the delays to ease."
You can read our full report on the crash and closure here.