An experimental nuclear fusion reactor intended to lead the way to a safe and clean new energy source for the second half of this century was on Tuesday formally launched by the world’s leading economies.

At a ceremony in Paris, ministers from the European Union, the US, China, India, Japan, South Korea, and Russia signed the agreement to give the go-ahead for the €10bn ($13bn, £7bn), 10-year project, which will be built in the south of France.