"The investigation will seek to establish if the police action was proportional to the threat posed by the miners," spokesman Moses Dlamini said in a statement.

"It is still [too] early in the investigation to establish the real facts around this tragedy," he said.

Investigators were working with the criminal record centre and ballistics experts, and would focus on collecting all the relevant evidence to assist in the investigation.

The police ministry said on Friday that "over 30" people died, and the National Union of Mineworkers (NUM) said that 36 people were killed when police opened fire on protesters gathered at a hill near the mine on Thursday afternoon.

Another 10 people -- including two police officers, two security guards and three NUM shop stewards -- were killed in separate incidents since the start of an illegal strike last Friday.

The strike was believed to be linked to rivalry between the NUM and Amcu over recognition agreements at the mine. Workers also wanted higher wages.

They claimed to be earning R4000 a month, with those living outside the hostel earning an extra R1000. Reported demands have included pay of R12,500 a month.

The workers had based themselves on a hilltop near the mine. Many of them were armed. They were shot when police tried to disperse the group.

A Sapa reporter on the scene said that after about three minutes of shooting, he counted 18 bodies lying on the ground.

Dlamini said IPID executive director Francois Beukman and a team from its national office would be briefed by an investigation team deployed at Marikana. He would then visit the scene.

Investigators from the IPID's offices in North West and Gauteng had been "working around the clock" since the shooting, he said.

Meanwhile, more then 50 police vehicles and at least 60 policemen were visible at the mine on Friday, ahead of a police briefing on the shootings. Two helicopters were intermittently circling the area.

"Be careful," said a security guard, who was busy checking in local and international media gathering for a press conference led by National Police Commissioner Riyah Phiyega.

She was expected to reveal further details about the shooting.

Barbed wire added an extra layer of protection at the mine, which has been shut down for all except essential services.