A gang of bikers caused chaos on a city street after an event organised on social media.
The large group of off-road motorcycles and quad bikes brought Kirkstall Road, in Leeds, to a standstill on Monday evening.
Police closed the road until the group had dispersed.
Witnesses posted videos on Twitter and described the scenes as being similar to those in the Mel Gibson film Mad Max.
It was estimated that more than 50 bikes were involved in the incident and the road was believed to have closed for around 90 minutes.
A police helicopter also attended the incident, which was described by Twitter users as "madness" and "utter chaos".
A West Yorkshire Police spokesman said: "There's been a large number of off-road bikes and quads gather after it has been organised on social media.
"They've been riding up and down Kirkstall Road causing some disruption to traffic.
"We did have a closure in place on the road but that has been taken off now and everything seems to be returning to normal."
The spokesman said there was a large police presence at the scene but no arrests had been made.
It was not believed to be a protest.
West Yorkshire Metro tweeted: "Closure Kirkstall Rd from viaduct & BP garage due to a crowd with motorbikes and quad bikes racing up & down the road. Police on the scene."
Councillor Lucinda Yeadon, deputy leader of Leeds City Council, said police had identified "key individuals" from the motorcycle gang and that some arrests had been made.
In a series of tweets, Ms Yeadon said: "All specialist roads policing officers in West Yorkshire are currently in Kirkstall and helicopter.
"Police response being co-ordinated by neighbourhood policing team. Key individuals have been identified.
"Police have said priority is safeguarding of public. Evidence is being collected."
She added: "Some arrests have been made and (police) expect significant arrest activity over the next few days."
Ms Yeadon said the event had been organised by an individual who is being sought by police.
Later posts on social media reported the bikes had also been seen riding through the pedestrianised city centre.
The latest incident comes a day after the Metropolitan Police arrested eight men for failing to stop during a similar "ride-out".
Officers used tyre deflation devices to stop 17 motorbikes and three quad bikes on Sunday evening.
No riders or police were injured, the Met said.
Men aged 17, 22, 22 and 32 were arrested in Blackheath, south-east London, while two men aged 20 and 28 and a 16-year-old boy were detained in London Bridge, central London. Another 22-year-old man was arrested in Stratham, south London.
Superintendent Ade Adelekan, from Met Command and Control, said: "The recklessness of the riders involved endangered not only themselves, but other road users and pedestrians.
"This is totally unacceptable behaviour that tied up significant resources that could have been better employed in emergency situations elsewhere."