National Highways had already warned that two lanes of the southbound carriageway at Junction 14 for Stafford would be closed on Saturday while work to update the road to a smart motorway continues.
However, on Saturday the agency reported a crash a few miles further south between Junctions 14 and 13 shortly before midday.
National Highways said the collision had closed three of the four lanes for a short period, announcing at 12.04pm that all lanes had been reopened.
However, drivers were warned: "Delays of 25 minutes remain in the area, with four miles of congestion so allow extra journey time this afternoon."
The crash came on the same weekend that work was being done to strengthen the southbound carriageway in Staffordshire.
Two lanes near Junction 14 remain closed throughout Saturday and up until 9pm on Sunday when a third will be closed, leaving just one lane open to traffic.
All four lanes are due to be open again by 6am on Monday.
The lane closures are part of upgrades being carried out on a 17-mile stretch of the M6 between Junction 13 at Stafford and Junction 15 near Newcastle under Lyme and Stoke on Trent to make it a smart motorway.
A spokesperson for National Highways said: "To minimise disruption, we’re limiting the length of roadworks that we need for this work; however, we will need to close some lanes for limited periods of time.
"Please bear this in mind when planning your journeys, we're sorry for any disruption this may cause."
The M6 between Junctions 13 and 15 is one of the busiest sections of road in the UK, used by over 127,000 vehicles per day and suffers from heavy congestion and unpredictable journey times, especially during peak periods.