The crew onboard Team Japan has escaped unscathed after a frightening moment in testing for the next America's Cup.

A section of the boat's wing has broken suddenly while the syndicate was sailing against Oracle Team USA at the upper wind limit of the AC45.

Skipper Dean Barker says fortunately there weren't any injuries and they managed to get the boat back to the dock safely.

Barker says understanding how hard they can push the boat is a key part of being successful next year and they're fortunate they'll be back out sailing by the weekend.