Bishop Abel Gabuza of Kimberley was speaking as thousands of protestors demonstrated in Pretoria last week over alleged financial misconduct.
The protests come amid several allegations of corruption against the ruling African National Congress (ANC) party and its leader Jacob Zuma.
One involves the technology company Hitachi, who are claimed to have made improper payments to the South African government. Reuters says Hitachi paid to settle the case out of court. The ANC denies taking this payment.
Another involves claims the ANC paid a $10 million (around £6.6m) bribe to secure the 2010 Football World Cup, which the ANC also denies.
And the South African public prosecutor has accused party leader Jacob Zuma of taking an "excessive" $23 million security upgrade to his country home, paid for by the taxpayer. Mr Zuma denies this.
Bishop Gabuza told the Missionary International Service News Agency: "Rhetoric is not enough, incisive interventions are needed, this is a national emergency.
""We are convinced that the government of the African National Congress is not serious enough in its prevention and fight against corruption."
The ANC said in a statement that it welcomed the peaceful protests, and that it hoped people would partner with it in tackling corruption.
