A wave of violence against immigrants in Johannesburg escalated Sunday, leaving at least six dead on the inner city streets of South Africa's economic capital, police and witnesses said.

Since the beginning of last week, foreigners have been targeted by mobs carrying machetes and guns in some of Johannesburg's toughest areas despite pleas for calm and widespread condemnation from politicians.

"It's very tense," police spokeswoman Cheryl Engelbrecht told AFP, adding that overnight violence had left six dead, 50 people in hospital and a trail of looted shops and burnt cars.

An AFP reporter saw armed police recover the dead body of a victim midafternoon in the notorious Hillbrow area of the city. They fired dozens of rubber bullets to disburse gangs in the surrounding area.

South African President Thabo Mbeki announced Sunday that a panel had been set up to look into the xenophobic attacks and he urged the police to act firmly against the perpetrators, news agency SAPA reported.

"We hope that the panel and the police will work together and help us answer who is behind this," he was quoted as saying.

The head of the ruling African National Congress, Jacob Zuma, also condemned the violence -- the worst yet seen since problems began early last week in the run-down township of Alexandra.

State radio SABC put the total death toll of the week at 16, but police declined to confirm the tally to AFP.

"We cannot allow South Africa to be famous for xenophobia," Zuma said from Pretoria, the domestic news agency SAPA reported. "We cannot be a xenophobic country."

He recalled the role neighbouring countries had played in sheltering ANC members in their fight against the racist apartheid regime in South Africa.

"We should be the last people to have this problem of having a negative attitude towards our brothers and sisters who come from outside," he said.

The bulk of the immigrants who have flooded South Africa in recent years are from neighbouring Zimbabwe, with an estimated three million having fled the economic meltdown and political crisis in their country.

They are blamed by some locals for crime and unemployment. Some Zimbabweans claim they are also accused of being behind rising food prices.

Eric Goemaere, coordinator for humanitarian group Medecins Sans Frontieres (Doctors Without Borders) in Johannesburg, said the violence had intensified on Sunday, with victims describing gangs of youths raiding their homes and looking for foreigners.

"The situation today is even more tense that during the week," he told AFP.

"They (victims) say there are organised gangs of 100 to 300 youths who are breaking into homes, apartments and shacks."

"The violence is quite extreme: one woman was thrown out of a first floor window and fell on a car. There is an intention to kill."

In one incident on Sunday, a church where about 1,000 Zimbabweans have been taking refuge was attacked, he said, as well as a local police station that was providing shelter to foreigners.

Bishop Paul Very of the targeted Central Methodist Church told SABC radio: "We consider that the situation is getting so serious that the police can no longer control it."

Engelbrecht said about 300 people, mainly immigrants, were sheltering in a police station in the inner-city Cleveland area of Johannesburg, where the violence was concentrated overnight.

"Five have been killed. Two have been burnt and three were beaten to death," she told AFP of violence in Cleveland overnight.

"Fifty others were taken to various hospitals for gunshot and stab wounds."

She said another person was beaten to death in the Jeppe area where cars were also burnt.

"A lot of foreign people have been attacked," she added, saying the police had made 10 arrests on Sunday morning.

"Most of the damage has allegedly been done to property belonging to foreigners. A lot of shops have been broken into and several cars have been burnt."