The confinement came into effect at midday on Saturday and has no end date, regional president Quim Torra said.
“We take a step back to protect ourselves and we will take all the decisions to stop the contagion,” he said.
Around 209,000 people live in 38 municipalities across the Segria region in the west of Catalonia, whose capital is Leida.
The number of people with Covid-19 who have entered the University Hospital in Leida has tripled in the last ten days, according to Spanish newspaper El Mundo.
After earlier ruling out “selective confinements”, Catalonia’s minister of health Alba Verges said on Saturday: “It is essential to act in this way.”
When the lockdown comes into effect only people who work in the region may enter or leave, although movements by motorways and highways that cross the area will be allowed, provided they are not originating or destination in Segria, said Catalonia’s minister of the interior, Miquel Buch.
In addition to restrictions on movement, there is also a ban on meetings of more than ten people, both in private and public spaces.
The lockdown in Spain comes days after the UK also ordered a regional lockdown for Leicester after coronavirus cases spiked in the Midlands city.
In the last two weeks, Leicester accounted for 10 per cent of all new cases reported in the country. It will remain shut for at least a fortnight as restrictions continue to be eased elsewhere.