An overturned semi truck leaking diesel fuel and an unknown substance are causing serious slowdowns on southbound I-285 in Cobb County.

The crash happened at the height of rush hour near South Atlanta Road, traffic monitoring services report, and isn't expected clear until around 6:30 p.m. Fire crews report no injuries however HAZMAT is being called to the scene due to a substance leaking on the highway.

As of 4:40 p.m., 3 of four lanes are blocked heading south on the section of highway.

11Alive is working to gather more details. For the latest cover, check the 11Alive Traffic Page.