One of New Zealand's most durable stayers, Castletown, has died aged 31.

The gelding was trained by Paddy Busuttin to win 16 of his 103 races, six at Group One level including three Wellington Cups.

He also raced with distinction in Australia, winning the 1992 Caulfield Stakes and running third in that year's Melbourne Cup won by Subzero.

He lived out his days in a paddock in Cambridge where he died on Sunday.

"He certainly had a very good retirement. He was spoilt and was in very good condition, even at 31. He had a shampoo yesterday morning before he was put back into his paddock and had a heart attack that afternoon," Busuttin's Victorian-based trainer/son Trent told NZ Racing Desk.

"He was a horse that meant so much to so many people and especially to me. He was Dad's pin-up horse and the horse that gave me the racing bug, following him around in the big races."

A New Zealand Derby winner, Castletown won the first of his Wellington Cups as a four-year-old and was placed twice in the Sydney Cup.

"He was an iron horse, so tough and so genuine," Busuttin said.

"Obviously his most memorable win was his third Wellington Cup because by then he was an older horse and past his peak but he was just such a warrior.

"Some of his best runs were in the big Cups in Australia. He was third in the Melbourne Cup carrying 57kg behind Subzero and Veandercross, giving both three kilos, and he was second in the Sydney Cup giving Just A Dancer four kilos, then came back the next year and ran third under 59-1/2. He was a great horse."