John Lewis says it is receiving five orders per second on its website today, with Black Friday set to be one of its "busiest shopping periods".
Sales through mobile phones saw a particular increase with a 21% spike between 8am and 9am, it said.
The most popular products being sold today include:
The Sonos Play 1 speaker (selling "one every ten seconds")
The Lego Simpsons House
Marc Jacobs perfume
Sophie Conran crockery - its best-selling homeware product