President Jacob Zuma defended his leadership of South Africa and the ANC on Wednesday.

People had told him that he could not rule the country because he was not educated, he said in isiZulu at the National Union of Mineworkers' (NUM) national congress in Kempton Park.

"I knew what I was doing then and I know what I am doing now," he said.

"I am not here by mistake. The issue is how do we make South Africa succeed? How do we bring about prosperity in our country?"

Zuma took a swipe at people with big mouths.

"That task is not for many of the people who talk too much, that task is now in our hands," he said.

"I am not like people who come today and speak louder, who were not there when things were tough."

Without mentioning anyone by name, Zuma said he did not judge such people.

"And we have never judged them... I think we are kind because we have a deeper understanding of the destiny of our people, the destiny of this country."

Zuma is campaigning to be elected for a second term as ANC president at the party's 53rd national conference in Mangaung in December.

The NUM is a key constituent of the Congress of SA Trade Unions, which is part of the tripartite alliance, along with the ANC and the SA Communist Party.

Zuma, who was welcomed by a sea of delegates dressed in red and singing "uZuma, my president", called on the NUM to take more of a political role in the ANC.

"Workers cannot be spectators."

He said some people believed unions should not concern themselves with politics, but only with factory and work conditions.

However, workers were affected by state institutions such as the police and the courts.

"That says workers, therefore, cannot sit back and not influence the politics that shape the state."

Mineworkers played a critical role in the country as mining made a substantial contribution to the economy. Mineworkers had also made a significant contribution to the struggle.

"You are the engines of the economy as mineworkers and have always been, that is why your congress is so important," Zuma told delegates.

NUM members should be represented at all levels of the ANC and not see the party as something separate to them.

"You need to be there, not just at branch level but all levels including the national executive committee of the ANC."

Zuma pointed out that the NUM was among the first bodies to adopt the Freedom Charter "which indicated the political consciousness" the union had then.

For this reason, the NUM should play an active political role in shaping the second century of the ANC.

"You can't shy away. Other unions may be looking up to you to the usual, to give leadership."

NUM president Senzeni Zokwana earlier told delegates the congress was a significant precursor to political events this year, including the ANC policy conference next month and Mangaung.

"What we do or say here will have bearing on all of those."