Police were called shortly after 1pm and made four arrests for public order offences and breaches of coronavirus legislation.
Photographs taken shortly after 5pm show hundreds of youths remained outside the shop during this time.
Many did not appear to be socially distancing despite the coronavirus pandemic.
The group did eventually disperse following instructions from police.
In a statement the Metropolitan police said: “Police were called at around 13:09hrs on Saturday, 5 December to reports of a large group of people attempting to enter a shop in Brompton Road, SW1.
“Four males were arrested in total – two for affray, one for breach of Covid regulations, and another for a public order offence and breach of Covid regulations.
“The crowd have since dispersed.”
Onlookers took to social media to describe their shock at events.
One Twitter user asked: “Harrods what the hell is going on??
“We ended up leaving the store because of the sheer f**king mayhem inside and out.
“None wearing masks and none being challenged on it??? #COVIDIOTS.”
Another added: “If anyone’s thinking of going near Harrods Knightsbridge don’t.
“It seems like riot police everywhere.”
There were also reports on social media of disorder outside the Harvey Nichols store in Knightsbridge.
London is currently under tier two coronavirus restrictions.