South African investigators are probing the police killing of 34 striking miners, as the nation sought answers following the deadliest protest since apartheid.

Armoured cars and police trucks patrolled the area around London-listed Lonmin's Marikana platinum mine while a helicopter circled above the spot where officers opened fire on hundreds of workers on Thursday.

The killings have cut to the quick of South Africa's psyche, with searching questions asked of its post-apartheid soul. Newspaper headlines screamed "Bloodbath", "Killing Field" and "Mine Slaughter", with graphic photographs of heavily armed white and black police officers walking casually past the bloodied corpses of black men lying crumpled in the dust.

Yesterday more than 1000 miners were gathered nearby, while relatives visited the mine's hospital hoping to find out if missing loved ones were dead, wounded or in jail.

The crackdown left 34 dead, 78 wounded and 259 detained, but angry relatives say police and mine management have failed to produce a central register of the dead.

The toll came after 10 deaths attributed to rivalry between unions during the week-long strike to back demands for a wage rise.

Meanwhile, two separate investigations were getting under way in addition to one launched by the police, whose forensics experts combed through the scene for a third day.

The Independent Police Investigative Directorate has opened what is likely to be a lengthy probe into the deaths, in addition to a national commission of inquiry announced by President Jacob Zuma.

"There's various investigations, there's a lot of experts involved, it will take some time," police spokesman Dennis Adriao said. "We will give our full cooperation with any of the investigations into the very, very sad, tragic event."

The directorate said its probe would determine whether police gave a "proportional" response by firing live rounds into a crowd of workers armed mainly with machetes, spears and clubs.

"Workers must calm down and allow leaders to address their issues," said Sidumo Dlamini, president of the powerful Cosatu trade federation. "It doesn't matter which union you belong to. There is a crisis. Let's create a platform where people will be free to express themselves, free to say their demands under a normal situation."

The violence stems from a conflict between the powerful National Union of Mineworkers (NUM) and the upstart Association of Mineworkers and Construction Union (AMCU).

NUM has close links to the ruling African National Congress, having produced some of the party's top leaders, including Deputy President Kgalema Motlanthe and ANC secretary general Gwede Mantashe. But some fear the union is too comfortable in the corridors of power among the country new black elite.

"The NUM is seen as compromised toward the government and they are not seen any more as an effective union at the local level," said Dirk Kotze, a political analyst at the University of South Africa.

Lonmin said it would help identify and bury the 34 dead and pay for the full education of their children. But it noted the strike was illegal and called on employees to get back to work, saying: "A stable mining sector is vital to the economic future of this country."