The Johannesburg Magistrate's Court and the South Gauteng High Court in the city centre have been evacuated because of a bomb scare.

It is understood police are combing both buildings.

On Wednesday morning, Eyewitness News received two phones calls involving bomb threats at the courts.

The high court was adjourned to 2pm after being evacuated.

Police and members of a security company are guarding the entrance to the court while scores of people are gathered outside.

It is understood an anonymous caller phoned the court's switch board earlier warning of bomb on the premises.

Police sniffer dogs are being dispatched to search the building.

"We will search until we are satisfied that there is no bomb," said Superintendent Lungelo Dlamini.