Gatherings in New Zealand, Australia and Japan have kicked off the worldwide March for Science, a global movement defending the role of science in society and calling for evidence-based politics.

More than 600 pro-science satellite marches were planned around the world on Saturday, with the main event in the US capital Washington, DC expected to draw tens of thousands.

In New Zealand, hundreds of scientists and supporters marched in Dunedin, Queenstown, Christchurch, Wellington, Palmerston North and Auckland in solidarity with their colleagues in the United States.

"Recent policy changes in the United States and elsewhere have caused heightened worry among scientists," the organisers of March for Science New Zealand said.

#marchforscience in front of the Queensland parliament Brisbane. Society needs science to inform, invent, and innovate. No science no future pic.twitter.com/H5jTVen7n4 — Niko Sünderhauf (@nikoSuenderhauf) April 22, 2017

Organisers in the US say the march is non-partisan and is not aimed against US President Donald Trump or any politician or party, though the Republican US leader's administration has certainly "catalysed" the movement, according to honorary national cochair Lydia Villa-Komaroff, a molecular cellular biologist.

"There seems to have become this disconnect between what science is and its value to society," she told reporters this week.

"Fundamental basic science really underlies all of modern life these days. We have taken it so for granted."

Trump has vowed to slash budgets for research at top US agencies, including the National Institutes of Health, NASA, the National Oceanic and Atmospheric Administration, and the Environmental Protection Agency which could lose one-third of its staff if Congress approves the proposal.

Trump's head of the EPA, Oklahoma lawyer Scott Pruitt, also claimed last month that carbon dioxide is not the main driver of global warming, a position starkly at odds with the international scientific consensus on the matter.