A rescue operation was launched Monday to save two Italian sailors stranded on a crippled yacht in the middle of the Pacific Ocean, about halfway between New Zealand and Chile.

An oil tanker was diverted to their aid, but New Zealand's Rescue Coordination Centre said it was 800 nautical miles from the 10-metre yacht and would not reach them for three days, dpa reported.

The pair used a satellite phone to tell contacts in Rome that their yacht's mast had broken and was hanging over the side of the boat, and it had lost engine power about 3,000 kilometres from New Zealand.

New Zealand authorities, who have international responsibility for maritime rescue operations in the area, were alerted.

The men, one in his 60s and the other in his 30s, were reported to be experienced sailors and one is a yachting instructor, Radio New Zealand reported.

They were said to be maintaining regular contact with rescue officials and the tanker, which is expected to take them to Argentina.