Fitzroy Engineering is building an underwater restaurant. The front window and the top will be covered with thick acrylic. The door at the back leads to a staircase that goes up to dry land.

A Taranaki engineering company is building an underwater restaurant, only the second of its kind in the world, for a resort in the Maldives.

The restaurant will sit beside a coral reef several metres under water and will seat up to 24 people.

Fitzroy Engineering is diversifying away from the oil and gas industry because of the downturn in the energy sector, New Zealand Business Development and Marketing Manager Mark Arnold said.

"We have become very busy in the fabrication and erection of structural steel for commercial buildings and projects such as this."

The underwater restaurant contract is worth several million dollars, Arnold said.

"The engineering design work has been done by a company in Auckland and we've built it to their design with some of our own input. The weld quality is similar to what we would apply to oil and gas work as it's under water and has to withstand pressure."

Project manager Adrian van't Hof said the restaurant would be 18 metres by 5 metres and 13 metres tall.

"The top of the restaurant itself will be on the surface and looks like a hut. There is a boardwalk that goes across the water. Then, you go to this little hut, go down the stairs and end up in the restaurant under water."

The sides down to dining table level, and the top, which covers the restaurant, are 120 millimetres thick acrylic, so is see through, he said.

"It's very strong."

The bottom of the hull is 114mm thick steel. The 415 tonne structure will be loaded onto a specialist ship in February and taken directly to the Maldives where it will be lowered over the side to sit on eight steel piles, he said.

"It has legs that fold down. The divers will go down and locate it and then once it sits on the piles, we'll fill them up with special concrete."

Fitzroy Engineering will be involved with the installation, he said.

The restaurant will be open for business in May, 2016.

The only other underwater restaurant is also in the Maldives.