Police had to be called to manage crowds in supermarkets as hundreds of customers flocked to midnight sales on Black Friday.

Tesco at Silverburn in Glasgow was closed for a period as people clashed over discounted goods.

Sarah Coubrough wrote on Twitter: "Silverburn shut cos shoppers going mental with the sales. Think I'll stick to the online shopping today."

Emma Somers posted: "Police called to the Tesco at Silverburn cause folk are fighting over the bargains for Black Friday."

At another Tesco store in Dundee, police were called to similar scenes and a decision was taken by staff to shut the shop.

A statement from Police Scotland's Tayside division said: "For information the Tesco Extra, Kingsway West, Dundee has been closed at this time due to excessive numbers attending to purchase sale items.

"This decision was made by Tesco staff to ensure the safety of all their customers."

Black Friday was originally a discounting day in the United States immediately after Thanksgiving but has now become a key date in British retail in the run up to Christmas.

A number of shops across the UK opened at midnight, boasting massive discounts on a range of goods.

As well as the scenes in Scotland, police were called to supermarkets in London, Manchester and Cardiff.

Greater Manchester Police said at least two people have been arrested at Black Friday sales events already this morning.

The force said on its Twitter feed: ''Keep calm people!''

According to the boss of Currys PC World Megastore at intu Braehead, it was busier than Boxing Day.

Hundreds of people queued long before the store opened at 8am - two hours earlier than normal.

Shoppers made a dash through the doors to grab a bargain, particularly in televisions, iPads and game consoles.

Megastore director Felix Rocks said: "It was very, very busy first thing, but everyone was well behaved.

"After the first wave of shoppers who had been queuing before we opened, it just got busier and busier, and it was like that for the rest of the day.

"There has been a lot of hype about Black Friday and that has caught the imagination of the public.

"Add to that the really great bargains on the go, in their minds people gave themselves permission to go out and spend.

"People were taking advantage of the huge discounts to do their Christmas shopping. I reckon a lot of the items bought will be for gifts.

"The crowds of shoppers reminded me of Boxing Day - only busier."

Shoppers in Asda in Edinburgh snap up Black Friday deals. Video by Ian Georgeson.

Tens of thousands of shoppers turned out at other stores at intu Braehead centre with discounts of up to 50% on offer.

Acting marketing manager at the mall, Christine Macdonald, said: "As well as the queues at Currys PC World, we also had lots of people waiting for the Game store to open at 8am.

"It's been amazing with people turning up at the centre as early as 6am. But the early birds definitely got the bargains as there are some really good discounts on offer."