Faced with a budget deficit that’s likely to reach wartime levels, finance minister Tito Mboweni is rebuffing suggestions that the central bank help plug the hole.

SA’s budget shortfall is forecast to exceed 10% of GDP in the fiscal year to the end of March 2021 as restrictions to curb the spread of the coronavirus weigh on economic activity and sap tax revenue. The largest gap on record was 11.6% of GDP in 1914, followed by 10.4% in 1940...