JOHANNESBURG (AFP) - A South African court on Monday postponed the trial of a teenager charged with hacking to death four family members with an axe pending a psychological evaluation, police said.

The 14-year-old was undergoing tests in hospital after the murder of his mother, grandmother, brother and baby sister, said police spokesman Lungelo Dlamini.

He had been due at Benoni Magistrates Court, but will instead appear on Wednesday.

The boy is charged with hacking his victims to death in the early hours of Friday morning as they slept.

Two sisters, aged eight and nine, escaped during the killings and raised the alarm in Etwatwa, east of Johannesburg.

Police tracked down the boy by midday after he ran away.

The mother, 42, was found dead in the corrugated iron-shack the family lives in, while the three-month-old sister was found dead in a nearby field.

The grandmother, 58, and brother, 7, died in hospital.

The murder weapon has not been found.

Police have not disclosed a possible motive, but community members told radio's Eyewitness News the murders may have been part of a satanic ritual or related to drug abuse.

The teen's family told the radio they had disowned the boy.

"Even now I can't cope, because I have to take the kids and they have to stay with me," an uncle said, "There is no other family member. They are all dead."

South Africa has one of the highest murder rates outside war zones.

Around 16,000 people were killed between 2011 and 2012, according to official statistics.