Foreign-owned shops in South Africa have been attacked and looted in east Johannesburg, the latest in a series of xenophobic attacks.
A standoff developed in the city, with police forming a barrier between an angry crowd and foreign-owned shops.
The violence comes despite Thursday's rally against xenophobia in the coastal city of Durban, and condemnation from President Jacob Zuma.
At least five people have died in anti-foreigner attacks in recent weeks.
Migrants, mostly from other African states and Asia, have moved to South Africa in large numbers since white-minority rule ended in 1994.
Many South Africans accuse them of taking jobs in a country where the unemployment rate is 24%.
A crowd began looting foreign-owned shops in east Johannesburg on Thursday night. About about 200 foreigners took refuge at a police station.
Police fired tear gas and rubber bullets to disperse the looters and arrested 12 people.
A new standoff began in the eastern suburb of Jeppestown on Friday, as police sought to prevent people from attacking more shops.
Police used rubber bullets to disperse a group of migrants in Johannesburg who had armed themselves with machetes for protection.
Eyewitness: Raphael Nkomo, a Zimbabwean living and working in Johannesburg
What I saw when I was going to the shops on Thursday evening, it was so terrible.
A group of men were dropped from a mini bus, and all of them were armed with pangas, a [type of] very big knife.
They started chasing people, throwing stones at them. Some were even knifed.
We had to run for cover. We ended up in the shops, and the owners closed the shops while we were still inside until the police were called.
What I saw was terrifying, and if it continues like this by the time the government wakes up many people will be dead. It is very, very bad.
The acting Premier of the Gauteng province around Johannesburg, Qedani Mahlangu, called on "each and every South African who's a peace-loving South African to stand up and condemn this."
On Thursday President Zuma condemned the recent xenophobic attacks as "shocking".
"No amount of frustration or anger can justify the attacks on foreign nationals and the looting of their shops," he told parliament on Thursday.
Zulu King Goodwill Zwelithini has been accused of fuelling the attacks by saying that foreigners should "go back to their countries". However, he said that his comments had been distorted.
The police have established 24-hour centres to clamp down on attacks on foreign nationals, the BBC's Milton Nkosi in Johannesburg reports.
Several African states have said they are prepared to help their nationals return home.
Amid fears of reprisal attacks, energy and chemical giant Sasol said it would repatriate more than 300 South Africans working in Mozambique.
Official data suggests there are about about two million foreign nationals in South Africa, about 4% of the total population. But some estimates put the number of immigrants at five million.
Many South Africans are against the violence, but are also unhappy with the level of immigration and feel they are being undercut by immigrants from poorer countries, our correspondent adds.
At least 62 people died in xenophobic attacks in South Africa in 2008.
"Zimbabwe has to have its economy working again so that its citizens are not hunted like animals in foreign lands. The xenophobia is not only a shame for South Africa, but for the continent at large." - Zimbabwe's Newsday
"As Malawians, let us collectively take a stand to show our anger. For starters, let us boycott South African business empires." - Malawi's Nyasa Times
"The most worrying thing is that all of this in happened South Africa amidst the quasi-indifference from the authorities. It took a dozen days of deadly violence in Durban for the president to be roused to action." - Burkina Faso's L'Observateur