Thick ice and snow have caused further travel disruption in Western Europe, as transport networks struggle to cope with the busy Christmas period.
The Danish army was mobilised to help emergency services through heavy snow and, in the Irish Republic, Dublin airport was closed for a short period.
Freezing rain in Germany created thick ice on some main roads, and there were further snowfalls in France.
Driving conditions in parts of Britain were said to be "treacherous".
Delays and cancellations affected rail services in parts of Scotland, England and Wales.
But Heathrow, the world's busiest international airport, was operating a near normal schedule. Both runways reopened on Wednesday night for the first time since Saturday.
Armoured personnel carriers
Most of Denmark was affected by falls of up to 15cm (6 inches) of snow. In southern areas, the army sent out armoured personnel carriers to help the emergency services and police advised drivers to delay their journeys if at all possible.
People on the Danish island of Bornholm in the Baltic Sea were urged to stay indoors and media reports described roads as impassable.
A police spokesman told Politiken website that there were concerns for motorists who had become stranded as the emergency services had no means of helping them.
In northern France, the authorities placed a number of areas on the second-highest state of alert.
Heavy snow fell around the city of Amiens and flights at the two main Paris airports, Charles de Gaulle and Orly, were cancelled.
In Duesseldorf in western Germany a school bus crashed into a tree after colliding with a car.
The driver was seriously hurt and 19 children and five other adults were lightly injured, local media reported.
Police in areas of Lower Saxony in the north said there had been an "endless" string of accidents, with roads described as similar to glass because of the fall of freezing rain on icy surfaces.
The motorway between Berlin and Hamburg was said to be at a standstill and heavy overnight snow in the Magdeburg area left a number of motorists stranded.