PARIS (REUTERS) - Coronavirus has forced the closure of a dozen schools in mainland France just days into the new academic year, the government said on Friday (Sept 4), as Covid-19 cases surge in parts of the country.

Education Minister Jean-Michel Blanquer said the overwhelming majority of France's 12 million pupils had returned without any problems and that glitches were to be expected.

The school year began on Tuesday (Sept 1).

Pupils aged 11 and over must wear face masks at all times.

Attendance is mandatory, though schools can adapt to surges in local infections by limiting numbers for a few days or weeks - again forcing some parents to juggle work and childcare.

"It's just the third day, they've just started, and there are already (virus) cases," said Giancarlo Ambrosini, whose son's primary school in Paris' 16th district sent home two classes for a fortnight.

Though his son was not caught up in the closure, Ambrosini said he and his partner - who spent the spring coronavirus lockdown at his family home in Italy - would need to devise a backup plan were the school to close.

"We both work, so it's not easy."

Some parents and teachers' unions had voiced concerns that the virus could spread through classrooms.

"The dynamic looks terribly like what we experienced before lockdown," Jean-Andre Lasserre, head of School Parents' Union FCPE in Paris, said of the virus' spread in the capital.

"How will we ensure that parents who are put into self-isolation because of the children do not lose any income because they cannot go to work?"

The education ministry told Reuters that, for now, affected parents would have to take holiday. It said the labour ministry was working on a measure to ensure that one parent could take paid leave without sacrificing annual holiday.

France reported more than 7,000 new coronavirus infections on Thursday, nearing the record of 7,578 set on March 31.