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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A man, woman and a baby were rescued after the building set alight.
The duke was presented with the trunks by Australian presenter and Paralympian Dylan Allcott.
The Duchess of Sussex did not attend an Invictus event on Sunday.