At least three gold miners in South Africa were killed Monday after entering an abandoned shaft, its owner said, in the latest of fatalities to hit one of the country's largest mining firms.

The bodies of three out of five employees who had entered the disused shaft at the Kloof mine, 60 kilometres (37 miles) west of Johannesburg were retrieved, Sibanye Stillwater spokesman James Wellstead told AFP.

However, the National Union of Mineworkers (NUM) and the Association of Mineworkers and Construction Union (AMCU) reported a death toll of four miners.

"We only have three confirmed dead," said Wellstead, adding that rescue teams were still searching for the other two employees.

"At this stage we don't know why they were entering a non-operational workplace," he said.

Unions lashed out at the company, which has lately been at the centre of a number of tragedies at South African mines. According to unions, 19 deaths have occurred at various Sibanye mines across the country so far this year.

"It seems that disasters have become the order of the day at Sibanye Stillwater and... we are highly disturbed and angered by this as this company is leading the pack in terms of fatalities and the number of deaths per mine," said Peter Bailey, NUM's health and safety official.

"This is unacceptable as we don't sell our lives, limbs or lungs to the industry but our labour to provide for our families."

Earlier this year, 955 workers at another Sibanye gold mine were trapped underground for more than a day after a power outage caused by storm. They were rescued unharmed.

Sibanye Stillwater last year produced 43,600 kilogrammes (1.5 million ounces) of gold.