JOHANNESBURG  Violence against immigrants, like some windswept fire, spread across one neighborhood after another here in one of South Africa’s main cities this weekend, and the police said the mayhem left at least 12 people dead  beaten by mobs, shot, stabbed or burned alive.

Thousands of panicked foreigners  many of them Zimbabweans who have fled their own country’s economic collapse  have now deserted their ramshackle dwellings and tin-walled squatter hovels to take refuge in churches and police stations.

This latest outbreak of xenophobia began a week ago in the historic township of Alexandra and has since spread to other areas in and around Johannesburg, including Cleveland, Diepsloot, Hilbrow, Tembisa, Primrose, Ivory Park and Thokoza.

Amid so much violence, the police were spread thin, sending in squads of officers in armored vehicles. “We are using all available resources and will call in reinforcements if the need arises,” a police spokesman, Govindswamy Mariemuthoo, told reporters.