The crash was reported at 9:03 a.m. and involved up to six vehicles including a big-rig, the dispatcher said. According to KTVU, an unsafe lane change caused the accident.
At least two people were injured, but the extent of those injuries is not yet clear, Golden Gate Bridge Highway and Transportation District spokeswoman Mary Currie said. (Beth Spotswood at Eye on Blogs says the injuries were minor.)
The bridge, which was closed for about 30 minutes, has since reopened, but traffic remains extremely slow in both directions.
Bay City News contributed to this report.