A man on Saturday wrested a gun from a policeman, went on a rampage and shot dead two patients inside a South African hospital, police said.

He also seriously wounded the police officer from whom he seized the firearm in Cape Town.

The "patients were shot dead and a police official was seriously injured on Saturday evening inside a local hospital when a 40-year-old man took the firearm of a police official and fired several shots," police spokesman brigadier Novela Potelwa said in a statement.

Police had taken a suspect needing medical attention to Somerset Hospital, near the V&A Waterfront, a popular spot for both local and international tourists.

The man grabbed the policeman's firearm, shot him in the head and then gunned down "two patients who were in his proximity" before other police officers disarmed him.

South Africa has one of the world's highest murder rates for a country not at war.

Last year Cape Town's murder rate was by far the highest in the country, at 64 killings per 100,000 people, compared to Johannesburg's rate of 37. New York's was 5.5.