The controversial painting of President Jacob Zuma in the Goodman Gallery in Johannesburg has been defaced, gallery staff confirmed on Tuesday.

"One man painted a red X across Zuma's face and the second covered the painting with black paint," a gallery spokesman said.

Both the face and waist of the painting were covered in black paint and no longer visible.

The painting, called "The Spear" by Brett Murray and bought by a German collector for about R136,000 was damaged on Tuesday around 11am.

The two men were being held by the gallery security team. The police were on their way there.

The painting, depicting Zuma with his genitals exposed, has sparked a furore, and prompted the ruling African National Congress to seek a court order for its removal from the gallery.

There has been immediate reaction to the defacing on Twitter from the microblogging site's users.

@Faanfairlane asked, "Who spearheaded this attack on Zuma's painting?", while @DieWortel wrote: "Zuma-painting de-"faced". Aiming too high?"

User @chiefkazi_p approved of the defacing, tweeting: "Give the man who did it a Bells!", with @Sthibo saying something similar: "Kwaaa, those 2 men who defaced the Zuma painting deserve a Double brandy n Coke."

Tweeter ‏@GvanOnselen was unimpressed: "There'll be a temptation to dismiss this as funny. It is not. It is profound. South Africa's tolerance was tested and we failed."

@pfumos tweeted: "A young black man and an old white man just did Zuma a favour by defacing the spear."

‏Some users believed the artist benefited more than Zuma, like @OfentseZA who said: "Defacing the PAINTING just made it more valuable and "Louvre" worthy."

@buliebabes agreed: "Publicity stunt for the gallery #makingupconspiracies".