British billionaire Richard Branson is calling President Donald Trump very "naive" for withdrawing from the Paris climate accord, saying he failed to recognize that clean energy is cheaper than coal and oil and is going to create "massively more jobs."

The business magnate, climate activist and philanthropist questioned Trump's decision to put "America First" when there are no barriers to the world's climate.

He said on World Oceans Day that many supporters of the Paris agreement "cried" when Trump went against 99 per cent of scientists and business leaders.

Branson said "we wanted the United States of America to not talk selfishly but to talk about being part of this world which doesn't have walls, and help us ... save it."

He spoke to reporters and in an AP interview.