The actions of a woman who drove on to the route of the Plymouth Half Marathon have been described as "disgusting".
Lorna Empson, a marshal at the race, said the driver was trying to get on to a main road and claimed "there was no other way out" due to road closures.
"People were not happy with her, [and] I cannot blame them as she could have caused a serious accident," she said.
Local MP Luke Pollard said it was "very silly" in light of terror attacks where cars were used as weapons.
A spokesman for Devon and Cornwall police said: "We believe that no injuries were caused by this action.
"Officers from the roads policing unit are aware of this incident and inquiries are under way into this matter."
A spectator captured footage of the car pulling out of Hawkers Avenue in front of the runners on Sunday.
One said he was watching his brother run the race when he heard "shouting and a bang".
"[I] looked down the road and saw she'd pulled out in front of the runners. To begin with we thought she'd hit someone," he said.
"It just left me speechless, after the recent attacks on people using cars, you just worried as soon as you heard a bang and a car in the middle of a half marathon race."
GB sprint hurdler David King expressed his frustration on social media, describing it as "disgusting".
Disgusting behaviour 😱You need to watch the video to believe it 😂 why do some people think they are above the law and everyone else? 🤦🏼♂️ https://t.co/OSl1G3tiu9— David King (@DaveKing_) May 20, 2018
Mr Pollard, MP for Plymouth, Sutton and Devonport, added he was "glad no one was hurt".
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Ms Empson said other cars did approach the race route but no one else drove into the path of the runners.
This was not a very smart thing to do. Driving a car at pedestrians has been used by terrorists recently and runners and cars are kept apart for very good reasons. National embarrassment follows a very silly decision. Glad no one was hurt. #plymouth https://t.co/4osXhRbJeP— Luke Pollard MP (@LukePollard) May 20, 2018