Anti-migrant protests in two South African cities including Johannesburg's Soweto township turned violent on Thursday, with the government blaming disinformation over a court ruling on asylum seekers.

In coastal Durban, the second city hit by protests, a Reuters reporter saw five torched cars in the urban centre, where foreign-owned shops were also looted.

The unrest followed a protest by a group demanding that a refugee centre stop processing asylum applications.

In Soweto, a Reuters reporter saw residents carrying groceries out of a shop that they said was owned by a person from Somalia, whom they chased away. The looters fled after police arrived and made them disperse.

Government spokesperson William Baloyi said the violence was triggered by people spreading deliberately false information about a constitutional court ruling in July.

The country's highest court ruled that asylum seekers cannot be denied access to South Africa's asylum system solely for procedural reasons such as having entered the country illegally.

Baloyi said the ruling had been widely misrepresented and did not automatically grant refugee status, permanent residence or other legal rights to undocumented migrants. "We are deeply concerned by what is going on now," he added.

Police said in a statement that they had mobilised more officers in Durban, where they said at least 14 vehicles had been set alight while a guest house and warehouse were partially burned.

A top police official, Lieutenant General Puleng Dimpane, told a press conference in Soweto: "Those responsible for acts of violence and destruction will be identified, investigated and where sufficient evidence exists, arrested and brought to book."

Dimpane said 10 vehicles had been burned in Soweto but the situation was now under control.

South Africa has seen months of anti-migrant marches this year that have drawn international criticism.

Some of the marches have descended into violence and looting, and thousands of African foreign nationals have fled the country.

Migrants are often blamed for taking jobs, fuelling crime and straining public services, claims that social scientists say are not supported by evidence.

Three decades since apartheid ended, South Africa remains deeply unequal and about a third of people are out of work. Despite this, it remains Africa's largest economy and continues to draw migrants.