At least 17 people have been injured, some seriously, after two “boy racers” crashed into each other before careering into a crowd of bystanders.
Video posted on Twitter showed one car emerging onto the A602, in Stevenage, as another vehicle was approaching the junction at speed.
They then collided and rebounded into pedestrians lining the road and central reservation.
One witness said on Twitter: “I’ve just witnessed that horrendous crash in Stevenage, no more than 50ft away from me. I’m still trying to process it all.”
Hertfordshire Constabulary confirmed the number of people injured in the collision on Monkswood Way had risen to 17 on Friday morning, adding that it was not aware of any fatalities.
A spokesman said: “I am not aware of any fatalities or arrests at this stage, however investigations are ongoing.
“We are working with the road policing unit and local policing teams for further updates and will be in touch in due course.”
A group called Cruise-Herts had said on Facebook that it was holding a car meet event on Thursday to raise money for a charity supporting bereaved parents.
Organiser Rix Sidhu, 29, said the event had been running regularly for 17 years, providing a “safe space” for car enthusiasts to meet within a controlled, closed environment.
He said: “We are devastated. I’ve been running this for 10 years and we have never had one incident.
“We were raising money for charity, as we often do, and there was no speed element to it.
“We held the meet in a car park with a speed bump at the entrance. But unfortunately some people went a bit rogue.
“We try and stop that, we urge people - urge them on social media beforehand - not to go out on the roads, not to risk injury or anything.
“But unfortunately, in this age of social media and Snapchat, people want to get footage and post things to their friends, which seems to drive some people to the main road.”
Police have urged any witnesses to get in touch and have asked anyone with footage of the incident to email it to Optephraherts.pnn.police.uk.
Press Association contributed to this report
