Twelve people were arrested and one person injured after a protest turned violent in Riverlea on Thursday, Johannesburg police said.

Inspector Gordon Billing said protesters began demonstrating at 4am and police resorted to firing rubber bullets at the crowd when they became violent.

"We were caught by surprise this morning. We were not aware of any protest," he said.

The protests were over poor service delivery, including housing.

"We had to fire bullets as they began pelting cars with stones and were becoming violent... the one person who was injured in the shooting will be arrested as well."

Billing could not say exactly how many protesters were present at the time.

The crowd, since dispersed, were protesting on Nasrec Road near Soccer City, a major 2010 football world cup venue.

The road, which was blocked with burning tyres and rocks, had since been re-opened by mid-morning.

By 5pm, police were still monitoring the area.

"It was quiet and the Public Order Policing unit will continue to keep watch over night," said Billing.

He said police were not sure if the protest would continue on Friday.