Slovakia, a country of 5.5 million, ordered all but essential shops and services closed and banned people from travelling outside their districts unless going to work, school or a doctor.
Gatherings of more than six people were banned.
The decision comes as coronavirus cases surge across Europe, making the continent the centre of the pandemic again, and follows neighbouring Austria which started a lockdown on Monday.
In the city of Trencin, 130km north of Bratislava, musical instrument shop manager Roman Spatny said his income was tied to sales and would vanish with another lost Christmas season.
"For us this is a plain knife in the back. We have to be closed at a time that business-wise is the most important for us, same as last year," he said.
"Important decisions are taken from one hour to the next. There is no way to properly react to this."
Student Natalia Paskova, 17, saw little choice: "The situation is getting worse so the decisions are justified," she said.
The government initially announced new restrictions applying only to the unvaccinated on Monday, before opting for the general lockdown.
It said any loosening - to be assessed after 10 days - would apply to first to those who are vaccinated.
Slovakia reported more than 10,000 new cases in each of the past two days, the highest to date.
With 1929 average daily cases per million population over the past week, it has the world's highest incidence rate according to Our World in Data.
The country has the EU's third lowest vaccination rate of just 45.7 per cent of the population, versus an EU average of 65.8 per cent, according to the European Centre for Disease Prevention and Control (ECDC).
Hospitals have reached the limits of 3200 patients which the government said was critical to maintain care.
The health ministry has said it had started discussing possible help abroad.
Slovakia has reported 14,107 deaths since the start of the pandemic.
