Germany stands ready to help Japan with the "demanding" goal of phasing out nuclear energy by drawing on its own nuclear exit progress, a government spokesman said Friday.

Steffen Seibert told a regular news conference that it was a "big political and social task" to phase out nuclear energy but was worthwhile and reaped new technological and industrial benefits.

Germany decided in the immediate wake of Japan's 2011 disaster at its Fukushima nuclear plant to shutter its nuclear reactors by 2022 and ramp up the use of renewable power sources.

On Friday Japan announced it planned to phase out nuclear power by 2040 in an apparent bow to public pressure after last year's disaster, the worst atomic accident in a generation.

"You can imagine that Germany, which now has had some experience with the path towards the future of renewable energy, willingly stands beside all Japanese institutions with help in words and deeds," Seibert told reporters highlighting Tokyo had only just made its decision.

"The Japanese know -- what we, too, know -- that is a very big political and social task that they have posed themselves," he said.

"It's worth it for the nation which goes down this path. It creates new technological possibilities, it creates new industry export potential, but is definitely a very demanding task, as we could say from experience, he added.

Seibert also said he could see broad scope for Germany and Japan swapping advice and expertise.

Japan's move also brings it into line with Italy and Switzerland.

The German government has come in for criticism for what industry officials say is a cripplingly slow approach to its energy transition programme.