Eric Crampton, economist and head of research at the New Zealand Initiative think tank, said: "I choose to recognise half-masted flags as mourning the victims of the oppressive Saudi regime."
Amnesty International spokeswoman Margaret Taylor told the Herald that King Abdullah bin Abdulaziz' death on Friday was a chance for the New Zealand Government and world leaders to step up and take a stand against the "appalling" abuses under his reign.
"We need to challenge his successor to improve on human rights ... Women still can't drive and can't get a job without asking the permission of a male relative."
Saudi Arabia is the only country that prohibits women from driving and punishes people renouncing their Muslim faith with death.
A spokeswoman for the Prime Minister said he requested that the flag fly at half mast in accordance with the law and he received advice from the Ministry of Foreign Affairs.
One of the days on which the flag is to be flown at half mast for mourning under the NZ Flag Notice 1986 is upon the death of the head of state of any foreign country.
The actual order is made by the head of the Ministry of Culture and Heritage and covers the NZ Transport Agency, which is responsible for the harbour bridge's flags.
The same decision to lower flags on Government buildings was made in the United Kingdom and Australia, sparking outrage from critics in both countries.
On Saturday, Mr Key paid tribute to the King, saying: "On behalf of the people of New Zealand I would like to extend our sincere condolences to the people of Saudi Arabia at this difficult time, and acknowledge the contribution King Abdullah made to his country and to global affairs."
The Governor-General, Sir Jerry Mateparae, will travel to Saudi Arabia to represent New Zealand at the ceremony of condolences.
