ANC president Cyril Ramaphosa. Picture: Siphiwe Sibeko/Reuters

Johannesburg - Deputy President Cyril Ramaphosa on Thursday welcomed moves taken by prosecutors against companies accused of corruption and said the ruling party would impose the policy certainty needed to attract investment to the country.

He made the televised comments during a business breakfast ahead of the World Economic Forum in Davos next week.

Ramaphosa will lead the South African delegation there and said his "sole purpose" in going there was to "sell the country" as an investment destination.

Ramaphosa, who was elected president of the ruling African National Congress (ANC) in December, has been signalling a departure in style and governance from the scandal-plagued administration of President Jacob Zuma.

Zuma remains the head of state but faces a push from within the party to step down.

"The National Prosecuting Authority (NPA) has begun to move and we welcome that. We welcome the actions they are beginning to take and we encourage them to act with urgency," Ramaphosa said.

A State prosecutor said on Wednesday it had served a court order on consulting firm McKinsey relating to a R1.6 billion contract with state utility Eskom it worked on with Trillian, a local company then controlled by associates of Gupta family, who are close to Zuma.

Zuma and the Guptas have consistently denied any wrong doing.

"We want deal with the rot. It is unacceptable, totally unacceptable, that companies owned by the nation and set up to benefit the people, have been hijacked, captured, by certain interests," Ramaphosa said in some of his strongest comments yet on a widening graft scandal that has shaken investor confidence.

Ramaphosa also admitted that reversing damaging ratings downgrades would be a "mammoth task".