PARIS, April 18 -- Some of France's biggest organizations, including carmaker Renault and rail authority SNCF, have given 5G technology the ringing endorsement it has so desperately needed from the companies that are expected to use it.

Senior executives from companies in various sectors backed the next-generation mobile technology as a major spur to productivity and French industrial advantage at a conference in Paris today hosted by Orange, the French telecom incumbent that hopes 5G will become the next big growth opportunity for its own business.

Guillaume Pepy, the president of SNCF and chairman of Eurostar, said 5G technology would allow France's national rail authority to increase the number of trains running on today's tracks by 45...