A shopping outlet had to temporarily close after roads around an Oxfordshire town became gridlocked by Black Friday shoppers.
Thames Valley Police warned motorists to avoid Bicester Village after roads into the market town became completely blocked with cars.
Supt James Templer described it as a "one in, one out situation".
The force was working with Bicester Village to "try and alleviate the pressure", he added.
Bicester Village, which is open until midnight as part of Black Friday, has apologised for the inconvenience and advised shoppers to come in the evening instead.
'One in, one out'
Shopper Natalie Taylor, 33, travelled from south east London with her 16-year-old son.
She said: "It's so packed, there's queues for almost every shop. I've never seen so many security guards in such a small space.
"Most people like myself are surprisingly calm, however there's a few who aren't.
"The shops are messy, overcrowded and the car park has been permanently full since 11.30GMT at least.
"We have literally had to queue for everything, from the shuttle bus, to the shops, and the restaurants.
"It's not an easy shopping day."
Police, who are working with Oxfordshire County Council and the Highways Agency to solve the situation, said the scene was "very busy".
"After this has finished we will need to work with Bicester Village and others to see how we can learn from what happened today," Supt Templer said.
"No one sets out to create traffic congestion but it's clearly been far busier than Bicester Village thought it was going to be."
He advised residents to approach Bicester from the north or east.
The A41 and the A34 northbound from Peartree Roundabout are described as stationary.
The M40 is also affected, with very slow moving traffic between junctions 10 and 9 southbound.