The South African Reserve Bank says growth forecasts will likely need to be re-examined given the impact of widening labour unrest on the economy.
South Africa has been hit by a wave of wildcat strikes since August that has spread beyond the mining sector, threatened industrial relations and sparked a downgrade of the country's credit rating.
Deputy Governor Daniel Mminele told a JP Morgan investor seminar in Tokyo on Sunday that growth was expected to average 2.1% for the 2008-12 period, significantly lower than the 4.8% that was averaged over the previous five years.
The speech was posted on the bank's website.
Standard & Poor's cut its credit rating on Friday, citing the strikes and social tensions. Moody's downgraded South Africa in September.
Mr Mminele said the downgrades were disappointing, but some of the criticism was valid.