Large crowds have crowded shops on Black Friday - the day after Thanksgiving - seen as a hugely important day for US retailers at the start of the Christmas shopping season.

The name Black Friday refers to the day on which many retailers are thought to move out of the red and into the black - which means they are making profits.

This year Black Friday has been marred by violence, including at Walmart stores. In one incident shoppers used pepper spray to fight off other bargain-hunters, while others were robbed at gunpoint on their way home with newly purchased goods.

In a Toys 'R' Us in Fairfax, Virginia, these shoppers stood in line for more than an hour to pay for their Black Friday purchases.

In recent years shops have been opening earlier and earlier, with many retailers opening their doors at midnight on Black Friday - and some even before.

Many US stores will now open every day until Christmas Day.