A damaged rudder ended a Swiss yachtsman's solo-round-the-world voyage 800km west of Stewart Island today.

The Rescue Coordination Centre New Zealand (RCCNZ) coordinated the rescue of the man who got into difficulty in his 52-foot (15.84m) yacht Horizons.

The yacht reported steering problems in rough conditions on Sunday night. Its rudder had been damaged, making it impossible to sail or motor the vessel.

RCCNZ sent an RNZAF Orion search aircraft to assess the situation, then diverted cruiseliner Seven Seas Mariner away from its passage to Milford Sound.

The liner met Horizons about 8am and rescued the sailor from his crippled yacht.

RCCNZ search and rescue mission coordinator Dave Wilson said the rescue had been an international effort.

"The yacht was technically in Australian search and rescue waters, but was physically closer to New Zealand. We worked with the Australian search and rescue authorities to ensure we launched the best response."

Mr Wilson said the skipper was in good health and spirits and was now on board the Seven Seas Mariner, en route to Milford Sound.

The liner was due to arrive early tomorrow morning.

When Seven Seas Mariner departed the area, Horizons was still afloat 650km west of Stewart Island. As the abandoned yacht was a potential hazard to navigation, a warning had been issued by Australia.

Mr Wilson thanked the master, officers and crew of the Seven Seas Mariner for a successful rescue conducted in difficult circumstances.

"The professionalism and skill displayed were instrumental in the rescue being successful."