Quinton de Kock acknowledges South Africa's Cricket World Cup clash with New Zealand is effectively a "quarter-final" due to its must-win nature, yet the Proteas are feeling confident.

South Africa endured a miserable start to the World Cup, losing their first three matches and then only taking a point against West Indies due to no result.

A victory against Afghanistan kept the Proteas' top-four and semi-final hopes alive, but there is no room for error now, with South Africa four points adrift of fourth-placed India.

"It's a big game for us, but in saying that, our next three or four games that we have [are, too]," De Kock told a news conference on Tuesday.

"They're all going to be big games for us for the rest of the tournament. We're just going to have to go out there, keep our heads steady and play freely.

"Tomorrow is a quarter-final, I guess you could say. But if we do win it, it's another big game again.

"Obviously, it is a big game, but there's a lot more that we are focusing on also. We have to win all the games, not just focus on tomorrow.

"But in saying that, we know how good New Zealand are playing at the moment. They are a big team in World Cups. They always seem to step up. So it's going to be a tough one."

Of South Africa's mood, he added: "Before our first game that we played against England, we were in a pretty good space also then, mentally and with preparation.

"Then obviously, during the course of the tournament, after losing all the time, there's always a bit of a slump in being mentally strong. It's a long tournament, it's a tough tournament.

"Obviously, getting a win again has given us high hopes. So we are pretty confident at the moment. It's just about taking it out there and giving the guys a good show."