French President Francois Hollande greeted heads of state from more than 140 countries in Paris as a key climate change summit got under way in Paris. Flanked by UN Secretary-General Ban Ki-moon, Hollande stood in front of the conference centre near the Le Bourget airfield to welcome delegates arriving at the UN-brokered meeting, known as COP21.

"The fate of mankind is on the agenda at this conference," the French president told newspaper 20Minutes in an interview ahead of the talks. The suburb of Le Bourget was under virtual lockdown with tight security imposed in the wake of the Islamist attacks that killed 130 people in Paris on 13 November.

Roads have been cordoned off and traffic diverted to clear the way for US President Barack Obama, his Chinese counterpart Xi Jinping and leaders from another 145 nations that are expected to address the gathering on its opening day. Riot police vans surrounded the conference centre while police and plain-clothes officers patrolled the surroundings.

Hollande said that despite terrorist threats and matters of home and international security lingering over the summit, climate change was a too crucial an issue to be overshadowed. "After the attacks in France, we must deal with the emergency and respond to the terrorist challenge, but we must also act for the long term," he said in the interview.

COP21: What you need to know about the Paris climate change conference IBTimes UK

COP21, the 21st session of the Conference of the Parties, aims to strike a new world agreement on reducing global warming. It follows the 1997 Kyoto Protocol, which despite the large-scale effort, was fatally flawed by the non-participation of the US, China and India, the world countries with the highest rate of carbon-dioxide emissions.

In Paris, delegates for more than 190 nations will take over the negotiation table from head of states on 1 December and discuss ways to reducing greenhouse gas emissions, including cutting the cost of cleaner energy, aid to developing countries and investments in renewable energy up to the end of the summit on 11 December.

Thousands of people marched on 29 November to call for stronger action against climate change, with demonstrations taking place all around the world. In Paris, where a rally was banned over security concerns, hundreds of people placed pairs of shoes along the Place de la Republique in a show of solidarity with environmentalists taking to the streets elsewhere.

Clashes with police erupted as some protesters defied the Paris ban to formed a human chain along the route of the cancelled march. Some 317 people were detained, authorities said.

COP21 UN Conference Paris
French police walk outside the venue hosting the COP21 UN Conference on climate change, in Le Bourget MIGUEL MEDINA/AFP/Getty Images