A woman holds a placard with the message "I Have a Dream" as she attends a protest against slavery in Libya outside the Libyan Embassy in Paris. Philippe Wojazer/Reuters

French President Emmanuel Macron on Tuesday called for "massive support to evacuate people in danger" from Libya.

Speaking to university students in the Burkinabe capital Ouagadougou, Macron said that the mistreatment of migrants in Libya was "a crime against humanity."

Footage aired earlier this month by broadcaster CNN appeared to show a slave auction in Libya where migrants were sold for 400 dollars (about R5400) each.

The scenes, coming after months of denunciations of the treatment of migrants held in the North Africa country, caused outrage in African countries.

What was happening in Libya was "the last stage in the tragedy that we have allowed to develop along what I call the route of need," Macron said.

The French president said that at a Euro-African summit starting on Wednesday he would propose an initiative "to put an end to the strategy" of terrorists and people-traffickers.

Libya, mired in chaos since the 2011 overthrow of dictator Moamer Gaddafi, has become a main launching-point for migrants and refugees trying to reach Europe.

UN human rights chief Zeid Ra'ad Al Hussein has said that EU assistance to the Libyan Coast Guard's efforts to intercept migrants had made it complicit in their inhumane treatment in detention.

Earlier, protesters threw stones at a vehicle belonging to the French delegation in Ouagadougou, French presidential spokesperson Bruno Roger-Petit wrote on Twitter.

Broadcaster Franceinfo reported that a French military vehicle had also been attacked with a grenade the previous night.