The taxi was travelling from Port Elizabeth to Mthatha when the accident happened on Wednesday night, said Constable Thomas Mayoli.
"As the taxi overturned and rolled... people were thrown out through windows. Four passengers died at the scene and the fifth one died while being transported to hospital following the 7.30pm accident," he said.
The eleven critically-injured people, including the driver, are being treated at the Nompumelelo hospital in Peddie, and the Frere hospital in East London.
No other vehicle was involved in the accident and police are investigating the cause.
"Police are still waiting for the driver to recover before interviewing him," Mayoli said.
Sapa
Ebrahim Moolla and Hadlee Simons debate whether the BRT system is really the best solution.
Rebekah Kendal wonders what it will take before someone stands up to SA's schoolyard bullies…
Do you need a laugh? Then check out our offbeat stories from around the world...