Traffic was reduced to a crawl at the Joe Slovo bridge, on Wednesday morning, after a diesel spill, Johannesburg Metro police said.
Chief Superintendent Wayne Minnaar said that "what appears to be diesel" was on the bridge, which joins the M2-East and M2-West.
Metro police and emergency services were on the scene and were directing traffic.
He said that traffic was congested and ice on the bridge compounded the danger for motorists.
Minnaar said drivers should keep headlights on and reduce speed.