At least 19 people are injured—five critically—after a double-decker tour bus lost control and crashed into a construction site in San Francisco's popular Union Square on Friday, KTVU reports. It's unknown what caused the open-air bus to lose control, but it traveled several blocks afterward, hitting cars, pedestrians, and a bicyclist before finally stopping. According to ABC7, the bus was finally stopped by some scaffolding, which fell into the street. A witness says they saw people falling from the scaffolding.
KTVU reports at least three people were trapped under the bus after it crashed, and at least five cars were totaled as it careened down the street. Victims had to be extricated from four damaged cars, according to ABC7. NBC Bay Area reports there were approximately 30 people on the tour bus when it crashed. An investigation is ongoing into what caused the bus to lose control. (Read more tour bus crash stories.)