A police department spokesperson said one of the 57 people injured appeared to be in critical condition.
"People were thrown into the air and onto the ground," passenger Elizabeth Banta told CNN. "There were definitely many people on the ground who were not moving."
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The 17-year-old was trapped for 30 hours in Australian shrubland but there was no report of a road accident to help the search.
The expansion of the probe came as Jeremy Corbyn declared Carillion's demise a "watershed moment" that should end "rip-off privatisation".
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