A world champion water skier has died after after a high-speed fall in the Bridge to Bridge race on the Hawkesbury River, north of Sydney.

Sarah Teelow suffered serious head and spinal injuries after falling from her skis just after the start of the event on Sunday.

It is understood she went into cardiac arrest, and was resuscitated by emergency services and flown to Royal North Shore Hospital.

Ms Teelow had been placed on life support but died on Monday evening.

The national governing body for ski racing confirmed the 21 year old’s death, describing Ms Teelow as one of the sport’s most accomplished young competitors.

Ski Racing Australia chief executive Kristie Middleton says the cause of the fall is being investigated.

“The ski racing fraternity is deeply saddened by Sarah’s passing and extends its condolences to her family. Ski Racing Australia is co-operating with police and maritime authorities in their investigation,” she said.

Ski Racing Australia chairman Rick Love said on Monday it was not yet clear what went wrong.

“The competitor in question is a very experienced skier and has been a competitor for a long period of time in Ski Racing Australia,” he said.

“I don’t really wish to speculate as to the reasons behind the fall but we believe that the conditions were good and that the sea was slight and that the skier has just fallen from the ski.”

The boat’s driver said on Sunday that Ms Teelow fell after hitting the wake from another boat.

Skiers reach speeds exceeding 130 kilometres per hour in the race, which runs for 112 kilometres from the mouth of the Hawkesbury River to Windsor.

In September Ms Teelow was crowned the winner in the Formula 2 category of the World Waterski Racing Championships at Tenerife in the Canary Islands.

Afterwards she wrote about the challenges of the sport.

“Water skiing, as a competitive sport, is a lot more than just how fast the boat goes,” she wrote.

“You are limited by your ability and your fitness. It requires skill, balance, strength, endurance, determination and a lot of nerve.”

Mr Love has defended the sport’s safety record.

“I would not say that it is a dangerous race. Ski racing has been around for a long time, 60 years.

“We’ve got a very proud and strong history of running really safe events throughout Australia.”