An intensive search for missing Cape Town international rugby referee Carl Spannenberg resumes on Monday at Zeekoevlei, where he fell off a ski boat and disappeared.

A dramatic bid by a friend to save Spannenberg on Sunday nearly resulted in his death as he became tangled in weeds on the vlei.

Metro Rescue made his rescue their first priority, then spent two hours, along with police divers, searching for 42-year-old Spannenberg.

The referee and five friends were aboard the skiboat when the accident happened.

It is understood that Spannenberg fell overboard, but immediately signalled to his companions that he was fine and in no danger.

But when the boat circled to pick him up, he had disappeared.

Freek Burger, manager of referees at the South African Rugby Football Union, said: "It's not a good day for me.

"He was like a son to me. He was a promising referee and this is a sad day for us all."

Spannenberg was due to officiate at this weekend's sevens tournament in Durban.

Metro Rescue senior operations manager Ivan Naidoo said the rescue service had received a call around 6pm on Sunday.

"We dispatched a Skymed helicopter to the Aquatic Boat Club at Zeekoevlei immediately, but they could not see anything from the air. Our diving unit was also sent there."

According to witnesses who spoke to Naidoo, a close friend of Spannenberg, known only as JJ, swam out from the vlei embankment to save him.

Naidoo said: "But as the man swam towards Spannenberg, he was caught up in weeds close to the shore."

Naidoo said because Spannenberg had already been in the water for a long time rescuers had made it their first priority to find JJ.

"A skiboat was sent to the weed area and we found him 20m from the embankment, tangled in weeds. He was face down in the water with a life jacket on.

"I personally examined him, and he was in a semi-comatose condition, with mild hypothermia.

"We successfully revived him, kept him warm and monitored his vital signs."