Countries have a chance to choose a new path as societies begin to return to normal after lockdowns imposed to prevent the spread of the coronavirus, activist Greta Thunberg told an Earth Day event on Wednesday.

Thunberg, who shot to fame as a 15-year-old when she started skipping school on Fridays to protest over carbon emissions outside Sweden's parliament building, said the outbreak showed the need for long-term thinking.

"Whether we like it not the world has changed, it looks completely different from how it did a few months ago and it will probably not look the same again and we are going to have to choose a new way forward," she said.