Just one week after a third of French schoolchildren went back to school in an easing of the coronavirus lockdown, there's been a worrying flare-up of about 70 COVID-19 cases linked to schools.

Some schools were opened last week and a further 150,000 junior high students went back to the classroom Monday as further restrictions were loosened by the government. The move initially spelled relief – the end of homeschooling for many hundreds of thousands of exhausted French parents, many whom were also working from home.

But French Education minister Jean-Michel Blanquer sounded the alarm Monday, telling French radio RTL that the return has put some children in new danger of contamination. He said the affected schools are being closed immediately. French media reported that seven schools in northern France were closed.

The situation highlights the precarious situation the French government is finding itself in as it seeks both to reassure the public that the country is moving forward past the coronavirus and to react prudently to safeguard public health.

Blanquer did not specify if the 70 cases of COVID-19 were among students or teachers.

Given that the incubation period for the virus is several days, people are "likely” to have been infected before the reopening of the schools, he said.

France reopened about 40,000 preschools and primary schools last week, with classes capped at 15 students.

About 30% of children went back to school, Blanquer said. The government has allowed parents to keep children at home.

This week France is reopening junior high schools in "green” regions less affected by the virus, which do not include Paris.

Although the idea of children being silent "super-spreaders” has been largely debunked in recent analyses, last week France recorded its first death of a child linked to Kawasaki disease, a mysterious inflammatory syndrome that some doctors say could be triggered by COVID-19.

The 9-year-old boy in Marseille was one of 125 children in France currently with the syndrome.

French authorities have reported at least 142,411 people infected with the coronavirus and 28,108 deaths.