Congestion stretched back at least 13 miles, the agency tweeted, warning of an hour-long waiting time.
Three southbound lanes were also closed.
All lanes reopened around 4.30pm.
The Central Motorway Police Group advised motorists to avoid the area.
“Please avoid the M6 Northbound between junctions 15 and 16, we are dealing with an incident there and traffic is at a standstill,” the CMPG tweeted.
“We will update you as soon as we can, thank you in advance for your patience and understanding.”
The group later tweeted: “We have opened one lane to allow traffic to pass. Thank you for your patience.”