Around 15,000 workers have downed tools in South Africa at a Gold Fields mine west of Johannesburg, just under a week after a strike ended at another part of the same mine, the company said Monday.

"Employees of the west section of the KDC Gold Mine... on the West Rand in South Africa have been engaging in an unlawful and unprotected strike since the start of the night shift" Sunday evening, Gold Fields said in a statement.

"Approximately 15,000 employees are participating in the strike and all production at KDC West has been suspended as a result," it added.

"At this stage the reason for the strike remains unclear but we hope to gain clarity as soon as possible," said company head Peter Turner.

A week-long illegal strike by 12,000 workers at the KDC mine's east section ended on Wednesday. Workers had downed tools in protest against their union leadership.

The Johannesburg strike follows a deadly wildcat strike at platinum giant Lonmin's Marikana mine almost three weeks ago, which left 44 people dead, 34 of them shot by police in a crackdown. The violence has been blamed in part on union rivalry.

Gold Fields, which is listed on the Johannesburg and New York stock exchanges, produces 3.5 million gold equivalent ounces a year, according to its website.

The company operates eight mines in Australia, Ghana, Peru and South Africa.