Rebel miners blockaded more than 400 workers underground in a South African gold mine Friday while 250 staged their own protest in a platinum mine, company and union representatives said.
The 447 gold miners were being held below ground east of Johannesburg in a near repeat of a three-day incident in October, the operator said.
The latest incident follows the murder this week of a company investigator who had looked into the earlier protest, said Ziyaad Hassam, head of legal at the Gold One mine in Springs.
A small group of balaclava-wearing employees was behind the "hostage situation" that began at the start of Thursday's night shift, he said.
The rebels had taken control of the miners' security access cards "so they are not able to get out from underground," Hassam told AFP.
Two miners who managed to escape early Friday confirmed the events to the management.
More than 500 miners were trapped underground for almost three days at the same mine in October during a standoff between rival labour unions.
Hassam said the reasons for the new incident were not immediately clear but the company suspected a link to disciplinary hearings over the previous incident.
Fifty workers were dismissed after the hearings ended on Thursday, he said.
A company investigator involved in the disciplinary process was murdered this week, Hassam added, without giving details.
Police were at the scene to monitor the situation, police spokeswoman Dimakatso Nevhuhuwli said.
Separately, about 250 miners demanding better wages entered the third day of an underground protest at a platinum mine west of Pretoria, according to the National Union of Mineworkers (NUM).
"Workers want salary increases," NUM spokesman Livhuwani Mammburu told AFP, confirming the strike at the Rustenburg mine.
Other complaints include unpaid maternity leave and the looming loss of hundreds of jobs at a time where the mine was advertising for senior roles, Mammburu said.
More than 20 miners suffering from chronic illnesses came to the surface on Thursday but the rest remained underground, he said.
The ministry of mineral resources said it was deeply concerned at the "growing trend" of underground protests.
"This poses a serious health and safety risk that could result in injuries and loss of life," ministry spokesman Makhosonke Buthelezi told AFP.