The annual index by advocacy group Fashion Revolution - now in its fifth year - ranked 250 of the world's biggest brands according to how much information they disclose about their social and environmental policies, practices and outcomes.

Garment brands are under rising pressure from campaigners and consumers to improve conditions for some 60 million workers in their supply chains, and to end abuse and modern slavery in the industry.

H&M, C&A, Adidas, Reebok and Esprit topped the index, which was published ahead of the seventh anniversary of the Rana Plaza factory collapse in Bangladesh's capital, Dhaka, which killed about 1,135 garment workers and injured more than 2,000.

The collapse of the eight-story building in April 2013 sparked demands for better safety and working conditions in one of the world's largest exporters of ready-made garments.

"It is impossible for companies to make sure human rights are respected, working conditions are adequate and the environment is safeguarded without knowing where their products are being made," Fashion Revolution said in a statement.

"That's why transparency is essential," it added. "It is the first step in holding brands to account for the human rights and environmental impacts of their practices."

Max Mara, Pepe Jeans and Tom Ford - among at least 10 brands that scored zero points - did not respond to requests for comment on the index from the Thomson Reuters Foundation.

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On average, the brands measured in the index scored 23 percent - up two percentage points from last year - judged on 220 indicators including working conditions, living wages, forced labor, supplier disclosure and buying practices.

Fashion retailers continue to disclose more about their policies than how they actually put them into practice, with comparatively little information shared about outcomes or progress made to improve their supply chains, the report found.

A global coalition of 10 organizations that advocate on behalf of garment workers urged governments and brands on Tuesday to help workers and support employers during the coronavirus pandemic.

With Western economies struggling due to the crisis and stores in many countries closed, some brands have cancelled orders or demanded discounts in nations from Bangladesh to Cambodia.

The coalition said brands should work with factories on safety measures, pay for all orders and avoid cancellations, and called on governments to offer relief funds to workers.

"COVID-19 has had a devastating global impact on the garment industry," the organisations said in a joint statement.

"Most factory workers do not earn enough to take care of themselves and their families and lack any kind of safety net to get them through this crisis."