An underground fire has engulfed a platinum mine in South Africa, claiming the lives of four people.

In a statement released on Sunday, the owners said the blaze erupted on Friday at the mine near the city of Rustenburg, located some 120 kilometers (75 miles) from the capital, Johannesburg.

“The four employees were overcome by fumes while they were trying to find their way to safety,” said the Johannesburg-based Impala Platinum Holdings Limited (Implats), the holding company for a group of firms that operate platinum mines.

South African Mineral Resources Minister Mosebenzi Zwani also described the incident as “tragic,” saying, “The health and safety of workers is of paramount importance and should continue to be a priority in all operations.”

Meanwhile, the National Union of Mineworkers, the main trade union representing the sector in South Africa, said it was “deeply concerned about these fatalities” at the platinum mine.

South Africa is rich in mineral reserves and possesses a number of platinum, gold, diamond and coal pits. However, the country, situated on the southernmost tip of the African continent, has witnessed several mining accidents over the past years.

There are almost 6,000 mines in South Africa that companies have abandoned due to falling profits. The mines, which have ageing shafts and wells, attract people digging for nuggets of gold.