But, she added, school is likely as safe as any place you could catch Covid-19 as a kid at a family get-together on the weekend or in the park.
"We don't know because the virus is everywhere," she told esRadio. Ms. Díaz Ayuso did not say what scientific evidence she used to predict that the infection rate in children would be this high.
Madrid is once again the epicenter of the Spanish virus pandemic, accounting for almost a quarter of the 1,830 patients hospitalized in the country last week.
In response, Madrid is now requiring the examination of all teachers returning to school, as is the case in other regions.
The result on Wednesday was chaotic: huge queues of school staff outside of the fully occupied test centers forced the testing process to be suspended.
As the situation in Madrid worsens, some other regional leaders have voiced their concerns about allowing residents from the capital region to enter their cities.
Spanish Health Minister Salvador Illa ruled out the idea of blocking the Madrid area on Thursday.
In other developments from around the world:
Thailand has gone 100 days without a reported case of local broadcast, However, there is significant financial cost to succeeding in containing the spread of the virus. Thailand's last reported case of community transmission was confirmed on May 24th. Since then, hundreds of cases have been found in residents returning from abroad, but all were discovered during the required 14-day quarantine period. Thailand had reported 3,425 cases and 58 deaths on Thursday, according to a Times database.
India reported 83,883 new cases on Thursday, breaking his own world record. It has the third highest number of cases and deaths after the United States and Brazil.
The Czech Republic 650 new cases were reported Thursday, the highest increase in a day.
Turkey will place restrictions on weddings and other social events, while new cases are on the rise. The daily number of cases hit nearly 1,600 in the past week.
The coverage was written by Liz Alderman, Ilise S. Carter, Choe Sang-Hun, Patricia Cohen, Ben Casselman, Michael Gold, Christina Goldbaum, Kathleen Gray and Luis Ferré-Sadurní. Jacey Fortin, Ethan Hauser, Jennifer Jett, Juliana Kim, Sharon LaFraniere, Raphael Minder, Matt Phillips, Campbell Robertson, Eleanor Stanford, Isabella Kwai, Jim Tankersley, Katie Thomas, Lucy Tompkins, Neil Vigdor, Allyson Waller, Lauren Wolfe, Katherine J. Wu and Carl Zimmer.