Campaigners warn the end of the New START treaty on February 5 could unleash a new arms race between the world's top nuclear powers and encourage China to expand its arsenal.

"Any armaments control treaty that expires must be cause for concern for us," German Foreign Minister Johann Wadephul told reporters in Canberra during a visit to Australia.

"It shows how large the task is when it comes to building new trust in the world that can be a basis for new agreements."

China should be part of future arms control efforts, the minister said.

"China has to be included," he said.

"China keeps emphasising that they stand with multilateralism, they also have to show in the field of arms control that they are ready to show restraint and that they invest trust in international relations."

US Secretary of State Marco Rubio on Wednesday called for a new agreement that includes China.

"The president's been clear in the past that in order to have true arms control in the 21st century, it's impossible to do something that doesn't include China, because of their vast and rapidly growing stockpile," Rubio said.

China's nuclear arsenal is growing quickly, with an estimated 550 strategic nuclear launchers, which is still well below the 800 each that Russia and the United States have been capped at under New START.

France and Britain, treaty-bound US allies, together have another 100.