The New Zealand Government today condemned the violence and loss of life and would pass its concerns on to Israel.
Mr McCully said a New Zealand citizen was on board the flotilla.
"We understand she is now in Israeli custody but is safe and well. We are pursuing all the usual lines of consular activity to make contact with her."
New Zealand supported calls for a full investigation into the incident.
"I am taking immediate steps to communicate the Government's concerns over this incident to the Government of Israel," Mr McCully said.
Some reports put the toll higher saying 19 were killed.
"We support the calls made by other countries for a full investigation into the incident," Mr McCully said.
"Representatives from our Mission in New York attending the emergency meeting of the United Nations Security Council and we will continue to follow their deliberations carefully.
"New Zealand calls for restraint from all parties in dealing with the aftermath of this incident."
He said the violence showed the continued situation in Gaza was unsustainable.
"We urge an intensification of the efforts to find a solution to that, and the wider challenges in the region."
During the incident marines stormed aboard from dinghies and helicopters.
Senior Israeli defence officials said 10 activists died on the Mavi Marmara, a Turkish cruise ship carrying 581 people, after commandos came under fire, including with weapons that the activists had snatched from the boarding party.
Seven of the troops and 20 protesters were injured, the military said.
Israel imposed a communications blackout on those aboard the convoy and other accounts of events were not available.
It was unclear who the casualties were. A senior Israeli naval officer said most of the dead were Turks. The convoy also featured Americans, Israelis, Palestinians and many Europeans.
European nations, as well as the UN and Turkey, voiced outrage at the bloody end to the international campaigners' bid to break Israel's blockade of the Gaza Strip.
Its navy stopped six ships ferrying 700 people and 10,000 tonnes of supplies toward the Islamist-run Palestinian enclave.
