Some 6,000 people have fled a wave of attacks on foreigners in South Africa, which has left at least 13 dead, aid workers say.
"This is a classic refugee situation," Rachel Cohen from Medecins Sans Frontieres (MSF) told the BBC.
Many of those who have sought refuge in police stations and elsewhere are Zimbabweans, who have fled violence and poverty at home.
Up to three million Zimbabweans are thought to be in South Africa.
The BBC's Caroline Hawley in Johannesburg says the immigrants have become a scapegoat for social problems, such as unemployment, crime and a lack of housing.
Over the weekend, correspondents say central Johannesburg resembled a war-zone, as armed police used tear gas and rubber bullets to disperse mobs of South Africans looking for foreigners and looting foreign-owned shops.
"If we go back into the streets, they're going to kill us there," one Zimbabwean man in a police station told the BBC.
The front page of several South African newspapers on Monday shows a horrific image of a man being burnt to death.
The police say they have made more than 200 arrests for crimes including rape.
'State of emergency'
A church where about 1,000 Zimbabweans have been taking refuge was attacked.
Bishop Paul Veryn of the Central Methodist Church which was attacked told SABC radio: "We consider that the situation is getting so serious that the police can no longer control it."
He called for a state of emergency to be declared to halt the violence.
MSF spokesman Eric Goemaere said: "This reminds me of a refugee situation. I have treated bullet wounds, beaten people, rape victims, and the people are terrified."
The xenophobic attacks began a week ago in the township of Alexandra, north of Johannesburg, before spreading to the city centre and across the Gauteng region.
President Thabo Mbeki said he would set up a panel of experts to investigate the violence.
The leader of the governing African National Congress, Jacob Zuma, has also condemned the attacks.
"We cannot allow South Africa to be famous for xenophobia," he told a conference in Pretoria.
PHOTO CAPTION
The body of an unidentified man, who was killed during violent riots, lies in a street of the central Johannesburg neighborhood of Hillbrow.
BBC