A courthouse inspired by the life cycle of a pohutukawa is unique, but whether the new Supreme Court - designed by the architects who created Wellington's "Cake Tin" stadium - is to everybody's taste will be discovered after its official opening today.

Prince William is to open the new Supreme Court building in Wellington today on his first official duty representing the Queen.

It will be the first chance the public has to see the interior of the $80 million project - an unusual design shaped like a huge egg with 3-D diamond-shaped wooden panels lining the walls.

Roy Wilson, director of architect firm Warren and Mahoney which designed it, said the room was based on the pohutukawa cone.

It linked with the attention-grabbing metalwork of the exterior to give the impression of looking out through the branches of the pohutukawa and rata trees, with dots of red stained glass as flowers.

The metalwork was made from recycled scrap metal and although distinctive, it has its critics - one onlooker said he would not give his verdict until the scaffolding came down.

Prime Minister John Key was luke-warm in his appraisal of the exterior, and said he would wait to see the inside today before making final judgment. He had heard a mixture of reports.

"I think it is an important addition to the landscape there and it's not for me to offer a view on the architectural merits or otherwise of the pohutukawa or whatever that are part of the facade on the outside."

Attorney-General Chris Finlayson was also reserving judgment, but said his main concern was not the building the court was housed in but the quality of its judgments.

However, Justice Minister Simon Power - who was recently shown inside - was more enthusiastic, saying it was a "unique and impressive building that is worthy of the top court in the land".

In Opposition, National baulked at the $80 million price tag of building the new court and restoring the old High Court behind it.

Despite the flourishes in design, Mr Wilson said, functionality was paramount. The wall panels were carefully angled to ensure good acoustics and the glass windows of the court could turn opaque at the push of a button in security scares.

A large skylight met the judges' requests for natural light. Large woven metal panels along the sides are designed to reflect tukutuku (woven panels in marae) and also hide audio- visual screens.

Despite the strong New Zealand flavour, some reminders of New Zealand's links with the Privy Council before the establishment of the Supreme Court in 2004 remain - the New Zealand Coat of Arms features in the new Supreme Court but the British Coat of Arms remains in the old High Court.

The new Supreme Court will also house a piece of "Queen's Silver" - a 17th century inkwell given by the Privy Council to the Supreme Court.

It will be displayed with an old wakahuia, provided by Te Papa.

The new building was completed last month and the judges have moved into their chambers on the second level, next to the library.

The old court was built in 1880 but closed in 1992 after falling into disrepair. It will be used for some specialist court hearings, but is unsuitable to house the Supreme Court because its Category A historical places rating mean it cannot be altered.

Its bench seated three judges - instead of five - and the Supreme Court does not need a jury area or prisoner dock.