Four 16-year-old girls were struck on Monday on their way back home from school.
BBC reports that five boys aged between 16 and 18 were admitted to hospital on Tuesday after a lightning bolt hit a cricket field at their school.
Nine school children are in hospital in the South African city of Johannesburg after being hit by lightning in two separate incidents, officials say.
More than 260 people are killed by lightning in South Africa each year
South Africa is prone to lightning during its summer rainy season.
According to the South African Weather Service, more than 260 people are killed by lightning in the country each year.
The lightning struck as the cricketers from King Edward VII School were pulling covers over the pitch after the storm began. Nine boys were taken to hospital and four were later discharged.
Education officials say two of the boys remain in a critical condition, as does one of the girls from Protea Glen Secondary School.
Following the incidents, South African Weather Service forecaster Puseletso Mofokeng said there was a common misconception that lightning mainly struck during heavy rain or a severe storm.
“There doesn’t have to be rainfall for lightning to strike, and when a storm is past it can still be dangerous,” the South African Press Association quotes him as saying.