The nude Extinction Rebellion demonstrators stood behind a banner that read: "Fast fashion costs the earth; rather go naked".

They had retailers including H&M, Zara, Cotton On, and Uniqlo in their sights, and walked into H&M brandishing the banner.

Police threatened to arrest the protesters unless they left the store, which they did after a few minutes before returning to the street.

The retailers encourage consumers to buy the "hot new look" at a low price, spokesperson Rosaria Burchielli said.

"These brands have accelerated clothing production. While promoting excessive buying and instant gratification to consumers, they have created a throw away culture," Ms Burchielli said.

"This means higher profits at the expense of workers and the planet."

The retailers that protesters targeted "have a particularly long way to go", and while brands say they are trying hard to improve their sustainability, they are "greenwashing", Ms Burchielli said.

The fast fashion business model is unsustainable because of its environmental impact, and governments and consumers need to hold the industry to account, she said.

The protesters chanted, "we're nude, we're rude; workers can't afford food", and "we're nude, we're rude; fast fashion means we're screwed".

They also chanted: "Fast fashion costs the earth; you won't get your money's worth."

Australian Associated Press