"We have to wait for the result of the post-mortem to find out what is his actual cause of death. Any speculation now is just that, speculation," Schutte told reporters at OR Tambo International Airport.

Schutte was among the group that climbed Mount Kilimanjaro as part of the Trek4Mandela expedition.

She said she was shocked to hear that Zulu had died when she returned from the summit.

"When we found out the next night that Zulu had passed, it was a shock to all of us. He hadn't really been ill. He had mild symptoms. Most of the people in the group were having the same symptoms."

Schutte said she had been treating Zulu's flu-like symptoms until he lost consciousness and had to be taken down Kilimanjaro on a stretcher to a nearby hospital.

"He was unconscious, but he had a strong pulse. I shouted we had to get this man down as soon as possible. He was in a critical condition. He was unconscious but he was stable. He was breathing on his own."

Schutte had expected that Zulu would reach a hospital in less than two hours. She never expected him to die.

"My expectation was that the team that ran down with the stretcher would get him down within an hour-and-a-half and he would start feeling much better. That is what happens with altitude sickness - as soon as you go down, you feel better."

Zulu, 38, died on Sunday. He complained of "flu-like symptoms" while ascending the mountain with his wife Letshego and several other South Africans. They had hoped to reach the summit on Mandela Day, July 18.

This year's Trek4Mandela expedition was intended to raise money to buy sanitary towels for needy girls across the country, to ensure they did not miss school during their periods.

- News 24.com