The numbers of coronavirus infections are back to levels seen in March when the virus gripped the continent, according to the head of the European Union's public health agency.

"The virus has not been sleeping over the summer. It did not take vacation," Andrea Ammon said on Wednesday, according to Reuters news agency.

Across Europe there are 46 cases per 100,000 people, she explained. In March there were 40 cases per 100,000, reaching around 70 per 100,000 by the end of April.

New cases now mostly involve young people, but she says that re-opening of schools does not necessarily pose a risk.