The Weather Office in Port Elizabeth has advised that the discomfort index has risen to "extremely uncomfortable" levels in large parts of the Eastern Cape.
By ten o'clock the index reached the 100-level or more in places like Uitenhage, East London, Bhisho, Port Alfred, Port St Johns, Fort Beaufort and Joubertina.
Weather Service spokesperson Garth Sampson says it is advisable to stop all school sport and strenuous activity in those areas.