The start of the US holiday shopping season was marred by shootings and pepper-sprayings as bargain-hunters stampeded stores.
The violence gave a whole new meaning to Black Friday, the day after Thanksgiving when many retailers move out of the red and into the black.
The incidents, including at least two robberies, mostly took place at branches of the store chain Walmart.
Half of the entire US population is expected to hit the shops this weekend.
Many stores had crowds rushing in as they opened at midnight - several hours earlier than they usually do - on the busiest shopping day of the year.
The openings were mostly peaceful, but there were ugly scenes in some places as crowds competed for goods.
One of the most dramatic incidents happened in a Walmart store in Los Angeles, where police are using CCTV footage to hunt for a woman who used pepper spray on crowds competing for Xbox 360s.
"They [staff] were opening a package to try to get some Xboxes from a crate and this lady pepper-sprayed a whole bunch of people in order to gain an advantage over the Xboxes," a local police sergeant said.
In the most violent incident, a man is in a stable but critical condition in hospital after being shot in the early hours as he left a Walmart with a group of people in San Leandro, California, when they resisted two armed robbers who demanded their purchases
Bargain-hunters were lured by an array of so-called "door-buster" deals of up to 70% off on big-screen televisions, video games and toys.
Analysts said that with the best deals focussed on must-have electronic items, demand - and competition - was strong and tensions were to be expected.
"The more the people, the more the occurrences," Marshal Cohen of market research firm The NPD Group told the Associated Press.
Occupy Black Friday
Target, Best Buy and Macy's were among the stores that opened at midnight, while Gap and Toys R Us opened on Thanksgiving itself.
Protests were planned in a number of cities urging people to boycott national chains on Black Friday.
Several Occupy activists demonstrated outside New York's flagship Macy's, but they could not put off more than 9,000 people who had queued for the store's midnight opening.
Nelson Sepulveda, a New York building superintendent, was the first in line at a Manhattan Best Buy store having queued for 28 hours before it opened.
He wanted to get his hands on a 42-in LCD television for $200 (£130) and other items, Reuters news agency reported.
For the past six years, a combination of increasingly early opening times and enticing deals have helped make the day after Thanksgiving the biggest shopping day in the US.
About 152 million people were expected to visit stores in search of bargains this weekend - up 10% from last year - according to the National Retail Federation (NRF).
But despite the large crowds, some expert observers said there was no indication spending levels were particularly high, noting that teenagers made up much of the crowd at the huge Mall of America complex in Minneapolis.
Consumer spending accounts for about 70% of US economic activity, so economists will be watching the retail bonanza closely.
Between 25-40% of annual US retail sales take place during November and December.
Analysts say a powerful start to the shopping season could cheer employment prospects in the retail sector, which supports about a quarter of all jobs in the US.
Retail hiring for the season has still not yet rebounded to its 2005 pre-recession peak of 642,000 workers, according to the NRF.