A 16-year-old with no underlying health problems becomes France's youngest COVID-19 fatality, shaking a nation hit by a spiraling health crisis.

"We'll never know why," the girl's mother Sabine told Agence France-Presse (AFP) late Thursday after France's national health director gave the latest grim toll from the outbreak, now at nearly 1,700 deaths.

For many people, the high school student's death brought home what experts have warned, the new virus is not a threat only to the elderly or people with underlying medical problems.

Earlier this week, the reported deaths of two young people with no pre-existing health conditions from the novel coronavirus in the U.S. and the U.K. have raised safety warnings.

A 21-year-old woman was reported dead on Wednesday from the disease caused by the coronavirus despite having no underlying health conditions.

In the U.S., another unidentified youth without pre-existing health conditions, from Lancaster, just north of Los Angeles, California tested positive and died.

Young people are not immune from the coronavirus and must avoid socializing and communicating it to older, more vulnerable people, the World Health Organization (WHO) has warned.