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The incident was reported just before 4 p.m. on the highway near the Cesar Chavez Street off-ramp, CHP officials said.
Initial reports said a dump truck had overturned and its driver was pinned underneath.
A San Francisco Municipal Transportation Agency bus was somehow involved in the collision, the CHP and San Francisco Fire Department said.
At about 4:40 p.m., fire officials said on social media that one person suffered critical injuries and five people suffered minor injuries.
At least two lanes of the highway's southbound lanes are blocked, according to the CHP.