Frustrations over rising prices and poor living conditions and resentment at a flood of immigrants from other parts of Africa have sparked some of the most chilling scenes in South Africa since the end of apartheid, with at least 20 people killed and hundreds wounded in several days of mob violence.

Police fought running battles with protesters in townships and informal settlements just east of Johannesburg’s city centre for the third day running on Monday. Aid workers said more than 5,000 people had fled their homes and sought refuge in community centres and police stations across the city since the attacks began in the northern township of Alexandra a week ago.