The four firefighters who were trapped in a burning government building in Johannesburg's city centre earlier on Wednesday have been rescued.

Two more firefighters remain trapped in the building while one fell and died during a fire fighting exercise in a building on Pixley Seme Street. Johannesburg Emergency Services spokesperson Nana Radebe said they were still conducting a head count to ascertain that all employees were evacuated.

The team of firefighters was trying to put out a fire on the 24th floor of the building that houses three government departments - the  departments of health, local government and human settlements.

Emergency Medical Services CEO Lesiba Malotana said it looked like the fire was caused by an electrical fault. 

Malotana said the fire started at about 10am. He said the fire hydrants at the building were first used to fight off the fire but when it spread emergency services were called.