JOHANNESBURG (Reuters) - Gold Fields, the world's No.4 gold producer, said on Monday 7 December it had halted gold production at its key Driefontein mine following a series of earthquakes, which left two workers missing.

"Production at the entire mine has been halted following the sequence of earthquakes, that led to a fall of ground. Two workers are unaccounted for, there is a big search and rescue operation to find them," Gold Fields spokesman Julian Gwillim said.

Gwillim said it was unclear when the mine would resume production.

The first earthquake at Driefontein -- situated west of Johannesburg in the nearby town of Carletonville -- measured 3.4 on the Richter scale and hit at about midnight, Gwillim said.

Gold production at the mine fell by 11 percent to 25,814 kilograms in the 2009 financial year, due to major interventions meant to improve safety.