An appearance by YouTuber James Charles is believed to have brought Birmingham city centre to a standstill after 8,000 fans flocked to the Bullring.
The beauty guru was greeted by three floors of screaming supporters during his visit to the shopping centre at about 11:30 GMT on Saturday.
But motorists were stuck in gridlocked traffic from 15:00 until 19:30.
Drivers trying to leave car parks found they were stuck and some opted to abandon their vehicles overnight.
Suffolk Street Queensway, Navigation Street, and Hill Street were all at a standstill.
I can’t believe this is my life pic.twitter.com/TOvGjNsk5d— James Charles (@jamescharles) January 26, 2019
Celebrity vlogger Charles tweeted a video showing the crowds at the shopping centre.
On Snapchat, he said it was the biggest meet-and-greet session he had ever done.
"There were 8,000 sisters [fans] at the mall," he said. "We keep breaking records every single time.
"I will literally never forget today."
Some fans had begun queuing at 08:00 to see him - but it is believed only about 250 took part in the meet-and-greet appearance inside the Morphe make-up store.
Crowds of supporters blocked the aisles, bringing the shopping centre to a standstill.
On Snapchat, Charles said he had wanted to say goodbye to fans at the Bullring, but it was a "hazard" and he had to get straight in his car.
After discovering the traffic chaos caused, he tweeted a cheeky "oops".
At the scene: Tom Richardson, BBC News
Unlike the thousands of teenagers hoping to catch a glimpse of their idol, I'd gone to the Bullring on Saturday morning to shop.
The top two floors were filled with excited youngsters (and some slightly bleary-eyed parents). As fans passed the time posing for selfies and jostling for the best position, repeated security announcements begged them to stop pushing.
When James Charles finally stepped out into the shopping centre, the deafening scream that erupted wouldn't have sounded out of place at a pop concert.
Afterwards, more loudspeaker announcements pleaded with lingering fans to disperse: "James Charles will not be making any more appearances today."
But they didn't seem to be going anywhere.
For the rest of us, the spectacle made for a welcome, if bemusing, distraction from the standard weekend shopping trip.
"What's all the fuss about?" one man asked a security guard.
"Some bloke off YouTube," came the reply.
West Midlands Police had earlier said the gridlock was caused by problems with traffic lights at the junction of Bristol Street and The Horsefair.
But contractor Amey later said this was incorrect and the lights had been working all day.
Birmingham City Council said it was "analysing the data" to establish the cause of the congestion which would "help inform if any changes are needed to the network in future".
The authority added: "It must also be remembered there are several regeneration projects and related highways work ongoing at present too, so we would continue to urge anyone coming into the city to plan their journeys in advance and use public transport wherever possible."
Some shoppers criticised the handling of the event.
Richard Simon said it was an "absolute disgrace".
This was an absolute disgrace today— Richard Simon (@simonXavier2018) January 26, 2019
There could of been a crush .... There nearly was
And nothing on entry to the bullring today to say this was happening
Walked straight into it
Poorly organised and should be reviewed by everyone involved
Amber Molland-Allman, 20, who was shopping with friends on Saturday, said it was "ridiculously crowded".
"There was a lot of people, three storeys of just a queue, the escalators were closed and we had to go down [floors] through different shops," she said.
However, Ms Allman said the atmosphere was "excited" and "everyone was really happy". She said security was handled "quite well".
Who is James Charles?
He is a 19-year-old social media star from Bethlehem, New York.
He has a YouTube channel followed by almost 14 million people where he uploads make-up tutorials, reviews and challenges.
The beauty influencer makes millions of dollars via his own merchandise and clothing range and sponsored social media posts.
He calls his fans "sisters" and his fanbase "the sisterhood".
Last year, he released his own eyeshadow palette that sent millions of teens and make-up lovers into a tailspin as they tried to get their hands on it. The palette sold out worldwide within hours - twice.
West Midlands Police said no extra officers were sent to the Bullring, other than an additional operational support unit that had been agreed in advance.
The force added no incidents were reported and no arrests were made.
Stephanie Lacey, general manager at Bullring and Grand Central, said: "We understand there was some congestion in the city caused by roadworks but yesterday's event was hugely popular and many shoppers were delighted to have the chance to catch a glimpse of James Charles."
Drivers took to social media on Saturday evening to express their frustration at the traffic in Birmingham.
Stuck in traffic in Birmingham for over an hour, James Charles definitely has something to do with this 🌚😂💋— ItsSamm (@It_sSamm) January 26, 2019
If you're trying to get into or out of #Birmingham good luck with that, traffic is at a standstill. Haven't moved in an hour.— @caroleann (@CaroleAnn1982) January 26, 2019
Meanwhile, British, European and World medallist gymnast Luke Strong was attending the British Gymnastics National Awards at the Town Hall, and said it took three-and-a-half hours to travel 0.8 miles around the "Pagoda Island" traffic roundabout.
The event's start time was delayed by an hour due to the traffic, he said.
"We were just stuck on a roundabout so we couldn't just abandon my car," said Mr Strong.
"I always know that the traffic in Birmingham isn't the best so I usually get the train, but I thought I would be OK and give myself a lot of time, but when I hit that traffic I regretted it."
Birmingham traffic might be the worst thing in the UK 😭😭😭😭— Luke Strong 🤸🏽♂️ (@Luke_strong2) January 26, 2019