A school boy stabbed a fellow pupil to death with a sword at the Nic Diederichs technical high school in Krugersdorp on Monday morning, Johannesburg police said.

He also stabbed two gardeners at the school, said Captain Jacob Raboroko.

The matriculant, wearing a black balaclava over a face smeared with black paint, entered the school premises with the sword and stabbed and killed a boy just before school assembly,

"He stabbed one of the school kids in the neck and he died. He then went further and stabbed a gardener in the back and another gardener in the face. They were taken to hospital in serious conditions," said Raboroko.

Krugersdorp councillor Alex Raubenheimer said school children on the scene told him the boy was high on drugs and was dressed like Joey Jordison, the drummer of the band Slipknot.

"He said Satan told him to kill the children," said Raubenheimer.

After stabbing the gardeners, the boy threw the sword on the ground and his younger brother grabbed the weapon and ran away.

Teachers then took the boy to the principal's office.

"Apparently he said to the principal: 'Wat nou, meneer? '."

Raubenheimer said his friends said he was a quiet boy who kept to himself. "They said they all thought he was a nerd."

Raboroko said the matriculant had been arrested. He did not know the age of the boy who had been killed.

The police were at the scene, taking statements from teachers and school children.

Lessons at the school in Krugersdorp North have been suspended for the day. - Sapa