Overnight, the capital shivered in temperatures as low as -3C.
A Transport for London roadside CCTV camera was among the first to capture a blizzard on the A4 Sipson Road near Heathrow. By 11am, heavy snow was falling as far east as Plumstead, in Greenwich.
The hashtag “Narnia” was trending on social media as people shared images of their snowy neighbourhoods.
Mayor of London Sadiq Khan was also out enjoying the weather.
He posted a video of his family’s golden retriever Luna spinning around the garden as the snow fell.
“Luna is loving the snow and hoping it settles,” he said.
One photo posted online showed a H13 bus struggling to make its journey through snow in Ruislip and a blanket over Clapham Common.
Highways England warned that the snow had caused collisions on the M3, M27 and M25. The agency urged drivers to only travel if absolutely necessary.
The Met Office was ready to put in place five new weather warnings for snow and ice going into the final week of January.
By 2pm, however, the snowfall had turned to drizzle in many parts of the capital, melting most of what was lying on the pavements and parks.
In flood-hit parts of the country, further heavy rainfall, which caused severe flooding in the wake of Storm Christoph, is not forecast until next Wednesday - but plummeting temperatures are expected.
Forecasters predicted the snow in would continue to fall in London until at least the middle of Sunday afternoon. Monday is expected to be dry and sunny - but the Met Office is warning of icy conditions with temperatures set to stay as low as 4C.
Temperatures across the whole of the UK dropped below freezing overnight, with the coldest temperatures in the Scottish Highlands at an icy -10C.
Elsewhere, London and Manchester got down to -3C overnight and Bristol, Belfast and Glasgow dropped to -2C.
Frosts are expected overnight on Sunday, Monday and Tuesday.
Meteorologist Martin Bowles said: “The biggest hazard over the next couple of days is going to be ice because we're getting these snow showers which will all freeze overnight.
“Obviously roads tend to be quite well gritted, especially main roads, but I would warn people to be careful on pavements, minor roads that don't get gritted or city roads."
Mr Bowles said the cold spell would continue until about Wednesday before being replaced with milder temperatures in the final days of the month.
“That's not to say that that's the end of all cold weather for winter, it isn't, we've just got a mild spell coming up,” he said.
Despite people being urged to heed flood warnings into the weekend, Mr Bowles said they were “gradually reducing” and that more heavy rain was not expected until Wednesday night or Thursday.
“We're hopeful that the river levels will fall quite significantly before that so we're not expecting any significant flooding problems over the next few days, apart from in areas where the warnings are already in place,” he said.
The Environment Agency previously warned of “exceptionally high river levels” following days of heavy rainfall in the wake of Storm Christoph, with hundreds of properties across the country flooded.