"What is the summit doing for us? It is providing for the rich, not the poor." - Protester Mathius Ledwaba
Singing apartheid-era songs, an estimated 20,000 people protesting about issues ranging from Aids to globalisation, arrived at the convention centre in the rich white suburb of Sandton from the shanty township of Alexandra.
At their head were some of the most radical groups - Muslims marching in support of the Palestinians, and members of the Landless People's Movement, demonstrating for jobs, land and everything they say they were promised before the change of government in South Africa.
Thousands of demonstrators have marched to the World Development Summit venue in Johannesburg, in the first mass protest to take place since it opened on Monday.
Police were out in force, with helicopters, dogs and water canon, but there had been no sign of any serious trouble by the time the rally began to break up.
Thabo Mbeki: Call to Action
South African President Thabo Mbeki, at a separate pro-government rally, described the eight kilometre (five mile) route taken by the march as a symbol of the "global apartheid" between rich and poor.
"We must liberate the poor of the world from poverty," he said. "It is easy for all of us to agree on nice words. Now has come the time for action."
Mr Mbeki did not join the main march and discouraged his ministers from doing so, for fear that radical protesters may cause violence.
A small wooden platform set up just outside the perimeter as a speaker's corner, was used as the stage for protest leaders to make their points within earshot of the delegates inside.
"Hello Sandton!...It's a pity you're barricaded, preventing us from coming in and showing you the real world!" organiser Virginia Setshedi yelled across the razor wire at the convention building.
"This just isn't good enough" - Hans Christian Schmidt, Danish Environment Minister
The crowd sang and danced as they waved banners with messages which included "Factory gases and waste are killing", "Hands off Iraq", "Globalise the Intifada", "Stop Thabo Mbeki's Aids genocide" and even "Osama bin Laden - Bomb Sandton".
Many chanted anti-American slogans and bore banners ridiculing US President George W Bush.
"What is the summit doing for us? It is providing for the rich, not the poor," protester Mathius Ledwaba told the Associated Press.
Inside the convention centre, meetings were going on to try to resolve fundamental differences between rich and poor nations.
There is concern that these will prevent delegates from approving a draft document before heads of state arrive next week.
Some representatives believe that if the final plan of action is not agreed by 4 September, when the summit is due to end, discussions could drag on for several more days.
Keen to avert a deadlock, South Africa - the summit host - has put forward a list of seven topics it says delegates should now focus on.
production and consumption
targets and timetables
access to energy
US intransigence is being seen by European countries as a key problem of the summit.
Washington is refusing to contemplate binding targets for introducing renewable energy technologies like wind and solar power, which do not pollute the planet.
Greenpeace has accused the US and Japan of horse-trading behind closed doors.
US delegates, it alleged, were offering to promote access to clean water in exchange for Japan supporting a removal of renewable energy targets.