S&P Global Ratings lowered South Africa's credit rating further into "junk" territory on Friday, citing the country's deteriorating public finances and weak economic growth outlook.

S&P dropped South Africa long-term foreign currency sovereign rating to "BB" after having placed it higher in the speculative category at "BB+" in April.

"Weak GDP growth has led to further deterioration of South Africa's public finances beyond our previous expectations," S&P said.

"We think the government will attempt to introduce offsetting measures in an effort to improve budgetary outcomes, but these may not be strong enough to stabilise public finances, and may weaken economic growth further in the near term."