Catalonia’s regional president Quim Torra told reporters there had been a “sharp rise” in infections in Segria, a zone that includes the town of Lerida some 150km west of Barcelona.
Nobody would be allowed to enter or leave the area, gatherings of more than 10 people would be banned and visits to retirement homes halted, officials said.
The move came as the summer holiday started in Spain and the country began re-admitting visitors from 12 countries outside the European Union, two weeks after allowing people from the EU’s visa-free Schengen zone and Britain to return.
Spain has been one of the countries worst hit by the coronavirus pandemic with 28,385 deaths, Europe’s fourth-highest toll after the United Kingdom, Italy and France.
It imposed one of the world’s strictest lockdowns to stop the spread of the virus and only recently began to open up.
Barcelona celebrated another milestone in its bid to re-open on Saturday, with visitors allowed back into the Sagrada Familia – an imposing modernist basilica that is among Spain’s most visited buildings.
In the first phase of its reopening, health workers were the first to be allowed back as a tribute to their work battling the pandemic.
On Friday, Spain registered 17 virus deaths within 24 hours, its highest daily toll since June 19.
The total number of cases now stands at 250,545 in a country of 47 million.
Lerida province, which includes the Segria area, has so far recorded just over 4,000 cases – 60 new infections were reported on Friday.