Some people could be stranded for days
Hundreds of cars were stuck for up to 17 hours overnight on roads between Cantabria and the province of Palencia.
Local media report temperatures of -15C (5F) and up 40cm (1.3ft) of snow.
Around 100 British expats and tourists were among those trapped. Spanish police rescued several stranded in their vehicles shortly after arrival in Santander by ferry from Portsmouth.
Many had come to Spain hoping for a warm-weather holiday, but ended up having to spend the night in the sports hall of a local school and the dining room of a hotel.
The country is in the middle of a cold spell that is expected to worsen over the next three days, with cold weather alerts issued for 20 provinces.
Spain's national weather service said in a statement that the unusually cold temperatures would last until next Tuesday.
The BBC's Tom Burridge in Madrid says that a large area of central Spain has seen an unusually high amount of snowfall in recent days.
One British woman, Jackie Elford of Margate, told the BBC she was driving to Marbella with her husband Roger when they were caught in heavy snow along with dozens of other motorists.
They were rescued at 03:30 (02:30 GMT) on Thursday, and spent the night on the floor of a hotel dining room in the village of Reinosa as there were no rooms available.
The couple have managed to book a room in the same hotel for Thursday night, but face postponing their journey south by one more day as the inclement conditions persist.
Abandoned cars and overturned lorries have piled up on main roads near Santander.
Spanish police said that dozens of military vehicles and snow ploughs are being used to clear the area.
Local media said that many schools in northern Spain had been closed and that there had been numerous power cuts.
El Pais newspaper reports that at least four towns in the region of Cantabria were still without power on Thursday.
Meanwhile, in Catalonia, winds of over 120km/h (75mph) have disrupted railway services.
Snowfall has also closed roads as far south as in Andalucia.
The freezing conditions are set to continue for several days, with the coldest temperatures expected on Saturday and Sunday, warned the national weather service.
Where is Mr. Gore, please? I want to talk to him.