|Automobile Association officials said conditions on British roads were treacherous [AFP]
Flights across Europe have been cancelled and road and rail transport made virtually impossible after blizzards and freezing temperatures shut runways, train tracks and highways.
Shivering drivers remained stranded on roadsides, while airports in Britain, Germany, France, Spain, the Netherlands and Denmark reported cancellations or delays to flights.
Heathrow Airport halted arrivals on Sunday and allowed only a handful of departures after snow and ice forced the closure of runways.
Al Jazeera's Andrew Simmons, reporting outside Heathrow, said "nothing is coming in; nothing is flying out".
"There's a plan to get out four long-haul and three short-haul aircraft today, but that's not certain. Thousands of people are completely stranded," he said.
A statement on the airport's website said a full reopening was scheduled for Monday.
"We are extremely sorry for the disruption," the statement said, urging passengers to check with their airline before travelling to Heathrow.
Several hundred workers were doing their best "to keep passengers in the terminal as warm and as comfortable as possible while we do everything we can to get Heathrow moving".
London's Gatwick airport reopened late on Saturday afternoon after 150 employees using dozens of ploughs worked to clear the runway of 10 centimetres (four inches) of snow, though officials warned flights would be limited and cancellations likely.
Ireland was battered by its worst snow in decades, but airports in Belfast and Dublin remained open while officials warned of cancellations and delays.
Al Jazeera's Sebastian Walker reports from London on the snow storm chaos.
Conditions on British roads were treacherous, Darron Burness, an Automobile Association official, said.
"One of the biggest problems is that large amounts of snow are falling very quickly on to frozen surfaces, making driving hazardous," he said.
Hundreds of motorists were left stranded on a major road in northwestern England following a deluge, prompting police patrols to offer food and water to drivers.
In Italy, the Autostrada of the Sun - the country's main north-south highway - was jammed with hundreds of vehicles, whose chilly occupants slept in their cars, vans or lorries. Though snow had mainly cleared or melted early on Saturday, the highway was still closed in one direction, with traffic backed up for 40km.
The snowfall also forced high-speed trains to bypass Florence's central Santa Maria Novella station, stopping in suburban stations instead.
Paris was sprinkled with a light coat of snow overnight, as many people prepared to set off on their Christmas holiday.
More snow on Saturday led civil aviation authorities to cancel 15 per cent of flights at Charles de Gaulle airport between 4pm (1500 GMT) and 11pm (2200 GMT).
Many flights were also cancelled in northeastern France, where snow already covered the ground, and services were also cancelled at the airports in the cities of Nantes and Rennes.
A large number of domestic and European flights were cancelled at Germany's Frankfurt airport as it dealt with the disruption.
Germany's railway operator Deutsche Bahn said it was pressing into service all the trains it could - though some journeys were subject to delays.
"Everything that can roll is rolling," Holger Auferkamp, the spokesman, told the German news agency DAPD.
The icy weather also swept over large parts of Scandinavia, causing problems particularly in Denmark, where dozens of flights were cancelled at the airport in Copenhagen.
According to Danish news agency Ritzau, train traffic between Denmark and southern Sweden was also disrupted because of track problems, partly due to the snow, forcing passengers to instead take buses between the two countries.
In Sweden, where media reports suggest the country is experiencing the coldest winter weather this early on in the season since the mid-1800s, several road accidents were reported, with more than 20 in the Stockholm area alone.
Retailers said the poor weather would affect their sales on what is traditionally the busiest shopping weekend before Christmas.