New Zealander Cameron Brown has been forced to withdraw from today's Ironman World Championship in Hawaii due to illness.

The 40-year-old, a 10-time Ironman New Zealand winner, was unable to start in today's race in Kona-Kailua after suffering from breathing difficulties.

"I've been suffering from the VOG [volcanic fumes] from the volcano here on the Big Island,'' Brown said.

"A lot of people have sore throats and allergies and I'm one of them. My whole family is coughing and have scratchy throats and I was hoping it would come right very quickly.''


However, this morning Brown was unable to breathe freely and was forced to withdraw from the race.

Brown had decided to return to Hawaii after his outstanding second placing in the Asia Pacific Championships and spent eight weeks training at altitude in Boulder, Colorado.

Ironman New Zealand winner Marino Vanhoenacker, of Belgium, has a five-minute lead in the men's race after the turnaround on the bike at Hawi.

In the women's race, Christchurch's Gina Crawford was third out of the water and is in the top-10 riding out to Hawi while Auckland's Jo Lawn is six minutes back.