"He was really assaulted very badly, he is still in a very serious condition in hospital," said Captain Anneke van der Vyver.
The protest in one of the biggest townships in the country was still continuing on Monday, she added.
"No violence was reported this morning [Monday]... the police are still in the area and they are making sure that people's lives are not endangered," said Van der Vyver.
On Sunday, the 35-year-old policeman, of Stellenbosch, and his friend were driving past the protesters on Landsdowne Road at around 6pm, said police spokesman Director Aaron Mlenga.
"The police constable tried to make his way through the crowd, but was stopped. The protesters took him out of his vehicle and assaulted him when he tried to make his way into the crowd," said Mlenga.
"It is believed that his firearm was taken from him during the scuffle," he added.
The Cape Argus newspaper reported that he was beaten up so badly that he lost consciousness.
Van der Vyver could not confirm that but said his injuries were very serious.
His friend, who was in the car with him, was also assaulted but not as badly. He suffered minor injuries and was not taken to hospital.
Anyone with information on the incident can call the investigating officer, Inspector Christa Swart, on 082-850-9791 or 021-360-2397.
Sapa
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