A correspondent for the South African Broadcasting Corp. said police at the Lonmin mine in Marikana, the world's third-largest platinum mine, first gave the strikers an order to disperse and then used stun grenades, tear gas and live bullets.
The correspondent said she saw about a dozen people down, either dead or too injured to get away.
"There are bodies on the ground -- I saw one with a bullet wound on the forehead," a witness told the BBC.
The wildcat strike began Friday with thousands of miners, most of them rock drillers, downing tools in a dispute about wages, SABC said. Some wives and girlfriends of the strikers joined them during the next few days, bringing traditional weapons and saying their families could not survive on what the men were being paid.
Before the shooting started, the National Union of Miners had said members were prepared to go back on the job.
Nine people were killed at the mine earlier this week, the BBC reported. The British broadcaster cited experts who said a feud between the National Union of Mineworkers and the new and more aggressive Association of Mineworkers and Construction Union was responsible for the shootings.