Thousands of people marched through South Africa's biggest city on Saturday, calling for an end to the violence that has killed at least 50 African migrants and forced tens of thousands to flee their homes.

Demonstrators carrying placards saying "Xenophobia hurts like apartheid" and "We stand against xenophobia" brought traffic to a standstill in Johannesburg's city centre.

People in the Hillbrow district, home to many African immigrants, cheered the march, which was organised by churches and labour unions.

Police said townships around Johannesburg were quiet but shops were looted and burnt outside Cape Town late on Friday.

The South African government has been criticised for its slow reaction to the violence, the worst since apartheid ended 14 years ago, and for not addressing the poverty that is widely blamed for the bloodshed.

President Thabo Mbeki said South Africans should not turn on other Africans and pledged that his government was committed to ending the violence.

"Today we are faced with a disgrace, a humiliation as a nation in that we have allowed a handful of people to commit crimes against other Africans living in our country," Mbeki said on visit to a mission school in the Eastern Cape province.

The violence started in Johannesburg's Alexandra township on May 11, and has spread to Cape Town and the eastern port city of Durban.

Police said at least 50 people had been killed in areas around Johannesburg. More than 25,000 had been driven from their homes in 13 days of attacks by mobs who have stabbed, clubbed and burnt migrants from other parts of Africa whom they accuse of taking jobs and fuelling crime.

FLASHPOINTS

Police said townships around Johannesburg were quiet on Saturday and in South Africa's premier tourism destination of Cape Town security forces were monitoring several flashpoints after anti-foreigner violence continued during the night.

Superintendent Andre Traut said shops were looted and burnt in Du Noon squatter settlement and in Kraaifontein outside Cape Town, as well as the city's largest township, Khayelitsha, where an estimated one million people live.

"Most of the incidents (on Friday night) occurred in Khayelitsha, where we had our hands full to protect the community," Traut said. Most foreigners left the area voluntarily or were escorted by police.

South Africa's foreign minister said on Friday the violence was embarrassing for the government and created a "very bad image" for the country. Nkosazana Dlamini-Zuma told Reuters in Moscow that the government would deal decisively with it.

Manala Manzini, head of the National Intelligence Agency, has said that people linked to former apartheid security forces are stoking the violence.

Earlier this week, Mbeki authorised the army to help quell the violence, which comes amid power shortages and growing social discontent which have rattled investors in Africa's biggest economy.

Officials in the tourism industry fear overseas visitors will stay away from a country that hopes to draw half a million extra tourists for the 2010 soccer World Cup.