UPDATE at 1:58 p.m.: all travel lanes on Ga. 400 southbound are now open.
Two travel lanes on Georgia 400 are blocked after a tractor trailer overturned just north of the Mansell Road interchange.
The closure is on the southbound side of the Hospitality Highway, and "is expected to be in place for quite a while," the city of Alpharetta posted on its Facebook page.
"There is currently no estimate as to when the travel lanes will reopen," the city added.
Motorists are encouraged to avoid the area and find an alternate route.