South African Paralympic athlete Oscar Pistorius has been arrested over the fatal shooting of his girlfriend at his home in Pretoria, local media say.
Police said a 26-year-old man, who they have not named, was in custody and a case of murder was being investigated.
The precise circumstances surrounding the incident are unclear. Reports say he may have mistaken her for a burglar.
Pistorius, 26, is known as the "blade runner", and was the first double amputee to run in the Olympics.
The incident is said to have taken place between 04:00 and 05:00 local time (02:00-03:00 GMT).
A police statement said that a 30-year-old woman was "fatally wounded" in the early hours of Thursday morning at a home in the Silverlakes complex in the Boschkop area of the capital.
The woman had been wounded in her head and upper body. Paramedics were at the house when police arrived, but she died at the scene. A 9mm pistol was recovered.
But the country also has a careful vetting process before awarding gun licenses, Erika Gibson of Beeld newspaper told the BBC.
Pistorius races wearing carbon fibre prosthetic blades after he was born without a fibula in both legs.
He reached the 400m semi-finals in the London 2012 Olympics. At the Paralympics he won silver in the T44 200m, gold in the 4x100 relay and gold in the T44 400m, setting a Paralympic record.
For years he dominated in his category at successive Paralympic Games.
The news that he may have killed his girlfriend will shock the country as Pistorius is regarded as one of South Africa's national icons, reports the BBC's Peter Biles from Capetown.