William, 28, and Kate, 29, who are gearing up for their wedding in April, signed together on one page of the book after returning from an official visit to St Andrews in Scotland, where they met while at university.
Harry, 26, was given a separate sheet of the black-bound book for his message.
The three sat at a table in the entrance to the building -- opened by Queen Elizabeth II in 1963 -- to sign the book. They simply signed their names but had previously sent a public message to New Zealand.
Prince Charles, the father of William and Harry, had already signed the book during a visit to the High Commission on Thursday.
"The royal family are also our royal family and so they are doubly welcome, hugely welcome," said Derek Leask, New Zealand's High Commissioner in London, after welcoming the royal party.
"It's touching that they are joining us to express their condolences and I am sure New Zealanders welcome that."
Queen Elizabeth, who is New Zealand's head of state as well as Britain's, has previously said she was "utterly shocked" at the 6.3 magnitude tremor, which flattened office blocks and knocked the spire off the city's iconic cathedral.
The queen is the monarch of 16 states, known as Commonwealth realms.
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