The Met Police have received several calls from besieged UK retailers as they prepare for unprecedented sales on Black Friday.
Police were called to four supermarkets in London as people gathered at Tesco stores in Edmonton, Willesden and Surrey Quays and an Asda in Capital Way, Edgeware. Many stores opened at midnight, touting huge reductions on goods.
Unconfirmed reports suggest clashes broke out near the Tesco shop in Edmonton. No arrests have been made and no injuries have been reported.
A Scotland Yard spokesperson said: "Police were called at 23.56pm to Tesco in Lea Valley, Edmonton, due to large crowds gathering outside."
''Officers have worked with store staff to ensure that sale-goers were able to enter and exit the stores safely.
''No persons have been injured at any of the locations as a result of the overcrowding."
Retailers are expecting record crowds as Britain embraces its biggest shopping day of the year.
This year Tesco has extended its Black Friday offers to select stores, after offering only online promotions last year.