South Africa great Dale Steyn has announced his retirement from Test cricket with immediate effect.

The 36-year-old played 93 Tests for the Proteas, taking 439 wickets at an average of 22.95 to become his country's most potent bowler of all-time in cricket's longest format.

Steyn said he has taken the decision to prolong his career, with the paceman contracted to play white-ball cricket for South Africa for the 2019-2020 season.

"Today I walk away from a format of the game I love so much. In my opinion Test cricket is the best version of this game," he said via a Cricket South Africa news release.

"It tests you mentally, physically, emotionally. It's terrible to consider never playing another Test again but what's more terrifying is the thought of never playing again at all.

"So, I will be focusing on ODIs and T20s for the rest of my career to maximise my full potential and ensure my longevity in this sport.

"I'd like to thank everyone in cricket, no one specific, because everyone has been a part of my journey. And I look forward to continuing to play for the Proteas in the shorter formats."

Steyn etched his name into the record books by becoming South Africa's leading Test-wicket taker in December 2018 when he dismissed Fakhar Zaman to beat Shaun Pollock's previous best of 421.

He has 696 wickets across all formats for South Africa and took a career-best 7-51 against India in February 2010.

The retirement of Steyn places further strain on the Proteas' fast-bowling stocks, with the likes of Duanne Olivier, Kyle Abbott and Morne Morkel having turned their back on South Africa to sign Kolpak deals in the County Championship.Cricket.

South Africa chief executive Thabang Moroe paid tribute to Steyn.

"Dale is undoubtedly one of the all-time greats of cricket. From the time he made his Test debut against England in 2004 and dismissed their captain, Michael Vaughan, with a superb delivery, he has been one of the standout fast bowlers in world cricket," he said."

He has led the South African attack brilliantly and set the standard for our future generations to follow.

"More than that he has been a wonderful mentor to our next generation of speedsters.

"We were saddened to hear of his decision, but it is one that management has to accept, and we thank him for his significant contribution to the sport and to the nation and wish him everything of the very best for the future."