A program to combat food waste and a scheme that pays citizens to restore natural ecosystems are among the five winners of Prince William's Earthshot Prize – receiving $1.37 million each to develop their environmental projects.

Sunday's ceremony was the inaugural event for the award, created by the UK royal to inject optimism into the fight against climate change and reward efforts to save the Earth.

The award will be given to five winners every year until 2030.

Speaking to young people, William said: "For too long, we haven't done enough to protect the planet for your future. The Earthshot is for you."

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"In the next 10 years, we are going to act. We are going to find the solutions to repair our planet."

The Italian city Milan won one of the prizes for its Food Waste Hubs program, which redistributes food that would have otherwise gone to waste to those in need.

Costa Rica won for its project that pays its citizens to restore the country's natural ecosystems.

The other prizes were collected by a joint Thai-German-Italian team, the Bahamas and India.

When attending the event, guests were asked to "consider the environment when choosing their outfit." And Harry Potter star Emma Watson wore a gown upcycled from 10-year-old wedding dresses purchased from the charity Oxfam.

Kate Middleton, Prince William's wife, wore a dress that was made for her in 2011 by Alexander McQueen.

Next year's event will be hosted in the U.S..

The award ceremony came days before the UK hosts the COP26 United Nations climate change summit, which Prince William, his father Prince Charles and the reigning monarch Queen Elizabeth II are planning to attend.

Several members of the royal family have recently become outspoken about climate change, although some activists in the UK have criticized them for not doing enough to fight global warming. 

For example, Chris Packham, a TV presenter and environmentalist, led a children's march to Buckingham Palace in London to present the royal family with a petition signed by 100,000 people that called on them to rewild their lands.