At least 28 fans and one driver were injured after a multi-car crash at the Daytona speedway when car debris flew into the crowd near the end of the Nationwide NASCAR race.
Race officials said 14 fans were sent to nearby hospitals, with another 14 being treated at the Florida speedway, which will host the prestigious Daytona 500 race on Sunday.
Driver Michael Annett of the Richard Petty Motorsports team was being treated at the Halifax Health Medical Center in Daytona Beach and would be kept for observation, the team said in a statement.
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In its first response since the 22-year-old's death, North Korea said Mr Warmbier was treated "according to international standards".
Police would face "real challenges" tackling a repeat of the London riots after years of cuts, one of Britain's most senior officers warns.
Here are the buildings we know are affected and what action is being taken by local authorities.