A 32-year-old woman has been arrested for murder after her 17-year-old niece was allegedly forced into a bathtub of hot water and killed, Pretoria police said on Wednesday.

Captain Daniel Mavimbela said the state of the girl's body in the bath so traumatised police officers who attended the scene, that counselling had to be arranged. 

He said the woman arrived at the police station on Tuesday night to report that her niece had killed herself.

However, while she was at the police station, police received information that this might not be the case.

"It is believed that, following an argument with the deceased yesterday [Tuesday] afternoon, the suspect allegedly immersed her niece in a bath of hot water inside their flat in Sunnyside," said Mavimbela.

Initial investigations led detectives to believe the teenager had suffered burn wounds to her upper and lower body, although a post-mortem will reveal the exact cause of her death.

The woman will appear in the Pretoria Magistrate's Court.