A wave of mass hysteria overcame a Pretoria high school as dozens of children collapsed, screaming in unexplained convulsions and fits.

The hysteria started when a Grade 9 girl collapsed at her desk at Daspoort Secondary School in Claremont on Thursday.

Within moments of the unexplained attack - the fifth to occur since February - about 25 pupils in various classes and grades were affected and started screaming hysterically, fainting and convulsed as they succumbed to the strange occurrence.

The attacks came two weeks after a pupil at the school committed suicide. It is said the hysteria affected schools in Sunnyside and Laudium last week.

The wave of hysteria, which gripped Daspoort soon after the school lunch break, saw teachers and prefects carry at least 10 pupils from their classrooms and corridors where they had collapsed, while others were evacuated to the school hall for safety.

Pupils were eventually moved from the hall to different evacuation areas around the school after another nine collapsed in convulsions inside the building.

It is believed at least six more collapsed after fainting or suffering convulsions as they fled the hall.

Many reported seeing visions.

At least one of the visions was believed to be that of the boy who committed suicide.

Megan Mabye, who collapsed outside the hall, said: "I remember hearing people scream and seeing a friend faint in the passage outside my classroom. I did not know what was happening. We were rushed to the hall where more children fainted and had fits.

"When we ran outside to escape, I fainted.

"I could see people around me and tried to get up, but I couldn't. My body was stiff," she said, fighting back tears as she described how she had a vision of "three green four-legged men" trying to kill her as a pastor stood over her, praying.

Megan's mother, Doreen, said it was clear there was an evil spirit around the school.

"How else do you explain what has happened. This is very worrying and scary," she said, adding that she had never believed in the supernatural until on Thursday.

Confirming it was the fifth "attack" since February, principal Gerhard Olivier said: "We are at our wits' end. We do not know what is happening or why this is happening."

He said the hysteria had gripped the entire school.

He declined to comment on the suicide, but said Satanism items had been discovered around the school recently and they were believed to be some of the causes.

Olivier, who fears that another attack could leave pupils seriously injured, said the school was desperate for a solution.

"Whatever is happening is very unsettling. We cannot explain it, except to say that it is clear that this is a sign of the moral degeneration which is occurring in our society.

"We are doing everything in our power to address the issue and have called in various religious people, along with psychiatrists and trauma counsellors to come and help our children," he said.

He was positive that what had happened at the school could be overcome with a solid Christian foundation.

"At the moment we have a seriously dysfunctional school with major discipline problems which we are urgently trying to address, and once we have this under control we should, hopefully, be fine," Olivier said, adding that in the past week at least two schools in Sunnyside and Laudium had been affected by similar occurrences.

Nick Dollman, Netcare 911 spokesperson, said the service had treated between 20 and 25 pupils at the school.

He said when paramedics had arrived at the school they had found several "patients" hyperventilating while others were having "seizures".

"At least 10 of the pupils were in serious condition and various medical tests were conducted.

"Police were also called to the scene and conducted drug tests on 10 of the pupils.

"Nothing medically wrong could be found with any of the pupils and all the narcotics tests were negative. Scientifically, we don't know what is wrong with these children," he said, adding that the cause of the hysteria was unknown.

Dollman said a trauma counsellor and various religious people were sent to the scene where they counselled the children.

He said the religious people, who had experience in unexplained phenomena, were usually called in for assistance when it came to matters such as the occult.

Gauteng Department of Education spokesperson Nanagolo Leopeng said the department was aware of what had happened at the school and was concerned.

"We are waiting for reports from the principal and the paramedics so that we can have a clearer understanding of what exactly happened.

"It is important to have the reports as we have to get to the bottom of this urgently, especially if it requires input from departments such as that of health," she said.

Commenting on similar incidents at other schools in Tshwane, Leopeng said the department would investigate.

"We will liaise with different education district directors to see how many other such incidents have occurred in Tshwane," she said.