DURBAN, South Africa (AFP) - South African swimming star Chad le Clos secured a place at a second 2012 Olympic Games event when he won the 200 metres butterfly Thursday at the national championships.

The 20-year-old is considered the second best swimming medal prospect in the South African team after Cameron van der Burgh and last Monday he bettered the 400m individual medley qualifying standard when winning the final.

Le Clos clocked one minute 56.17 seconds -- just inside the Olympic mark of 1:56.86 -- to achieve butterfly glory from Sebastien Rousseau and Dylan Bosch at the Kings Park pool in this Indian Ocean city.

"It is a huge honour to get another qualifying time but I am a little disappointed with my time," admitted a swimmer with his sights set on also qualifying in the 100m butterfly and 200m individual medley.

"I was hoping to at least match my semi-final time. However, I am halfway there now and I am just so happy with what I have achieved so far this week," beamed Le Clos.

The other male swimmer to better an Olympic qualifying time on the fourth day of the week-long championships was Gideon Louw, whose time of 48.74 enabled him to finish first in a 100m freestyle semi-final.

United States-based Louw was the fastest qualifier for the final ahead of 2004 Athens Games 4x100m relay gold medalist Darian Townsend (49.10) and Graeme Moore (49.53).

"It is great to have done this time," said Louw. "You train for practically four years to get here and it is such a relief to have bettered the qualifying mark."

Karin Prinsloo won the women's 200m freestyle final in 1:59.53, but it proved a hollow victory as her time was more than a second outside the time required for a ticket to the Games.

London-bound Kathryn Meaklim failed to better the Olympic mark when winning the 200m individual medley final in 2:13.64, but booked her seat on the flight to the British capital earlier this week in the 400m individual medley.

No South African swimmer won a medal at the 2008 Beijing Olympics and London hopefuls must match or better qualifying marks twice to book places with one of the times having to be achieved during the national championships.