Crowds were out and about in shopping districts of major cities on Saturday, including on London’s Regent Street, which had been temporarily pedestrianised to aid with social distancing.
Many shoppers spent time gazing up at the exquisite Christmas lights.
A joint statement from Mr Khan and Cllr Rachael Robathan, leader of Westminster City Council, said a “key” part of helping businesses recover from the crisis was “ensuring we get this deadly virus under control”.
“With cases rising in many parts of the capital, it is vital that we all work together to control its spread,” the statement said.
“Otherwise we may face tougher restrictions, which would greatly harm shops in the West End, our hospitality sector and the whole of London’s economy.
“We are appealing directly to Londoners – when out shopping it is essential that you follow the rules.”
Urging Londoners to wear a face covering in shops and socially distance from others, they advised avoiding travelling on public transport during rush hour and to walk and cycle “where you can”.
“If you have symptoms – don’t take a chance and don’t go out. Self-isolate immediately and get a test,” they added.
“Businesses across London have worked really hard to make their premises Covid-safe – but we must all play our part in following the rules. So this weekend shop safe.”
As of 9am on Saturday, there had been a further 21,502 lab-confirmed cases of coronavirus in the UK taking the total to 1,830,956 positive tests.
Increased infection rates have led to fears the capital could be headed for Tier 3 restrictions, which would see hospitality settings closed except for takeaway.
In an effort to tackle the spread in London, thousands of extra tests are being made available for schools in areas of concern.