The collision happened just after 11a.m. on Lombard and Fillmore Street, according to Robert Rueca with the San Francisco Police Department.
We were first told all six people have non-life threatening injuries, but in a tweet by fire officials around 4:30p.m., two are listed in critical condition, two moderate and two with minor injuries.
Witnesses say a speeding SUV slammed into the bus, and the impact sent the SUV into another car.
A passenger in the other car says a couple pedestrians were caught in between the vehicles.
One man was walking nearby when he saw the bus start to drive through the intersection after its light turned green.
"As it was going through the intersection about midway through the intersection, the Denali, the white Denali that was traveling westbound, was going...I would have estimated 80 miles an hour, but I heard it was even faster than that," said Hany Tawadrous, a witness.
"And it was a corner-to-corner collision, very bad as you can see from the damage, and the bus got spun around," he said.
A suspect driver has been detained, police said.
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