Pope Francis puts his shoes in the centre of Paris to protest against climate change

Activists laid out more than 20,000 shoes in the Place de la Republique to symbolize absent marchers on the eve of the summit

Pope Francis visits a refugee camp in Bangui on his current tour of Africa (AFP)

More than half a million people from Australia to Paraguay joined the biggest day of climate change activism in history on Sunday, telling world leaders gathering for a summit in Paris there is "No Planet B" in the fight against global warming.

In the French capital, where demonstrations were banned by the authorities after attacks by Isis militants killed 130 people on 13 November, activists laid out more than 20,000 shoes in the Place de la Republique to symbolize absent marchers on the eve of the summit.

Among the high heels and sandals were a pair of plain black shoes sent by Pope Francis, who has been a vocal advocate for action to prevent dangerous climate change, and jogging shoes from U.N. Secretary-General Ban Ki-moon.

One activist, dressed in white as an angel with large wings, held a sign saying "coal kills". About 10,000 people joined arms to form a human chain through Paris along the 3-km (2-mile) route of the banned march, organizers said.

Thousands of pairs of shoes at the Place de la Republique on the eve of the COP21 Conference opening (EPA)

French police detained scores of protesters after violent clashes in central Paris on Sunday though, a day before the official start of a conference that aims to tackle global warming.

Riot police used tear gas to disperse about 200 protesters, some of them masked, who responded by hurling rocks and even candles. French President Francois Hollande accused the violent protesters of dishonoring the memory of the dead.

The U.N. climate change conference is taking place at Le Bourget just outside Paris. Initial talks among negotiators began on Sunday.

More than 2,000 events were held in cities including London, Sao Paulo, New York and Asuncion, Paraguay, on the eve of the Paris summit.

About 683,000 people attended the rallies around the world, said Sam Barrat, a spokesman for Avaaz, one of the organizers.

"And this was done even without Paris," after the March there was banned, he said,

Around the world, activists marched, dressed as polar bears or penguins at risk from melting ice, or chanted slogans such as "climate justice"