Australian architects have won a prestigious international award for their reference design of the Sydney Fish Market, even though the $250 million project will be completed by another firm.

Michael Heenan's firm Allen Jack and Cottier and NH Architecture won the 2017 Future Project of the Year award, one of the largest prizes in architecture, for its reference design of the market.

The rethink of the Sydney icon included relocation of the markets and a large canopy, which extends over the public walkways in Blackwattle Bay.

The firms were contracted by the New South Wales Government to prepare the reference scheme and urban design framework as briefing documents for an international tender for the project.

The now-award-winning design was not tendered as part of that process.

The Danish firm 3XN was selected from a shortlist of six international designers and awarded the contract based on an indicative design.

Mr Heenan said he always knew the design was not going to be built.

He said he was employed by Urban Growth NSW Development Corporation to come up with a design, but knew the project would go out to public tender.

"Now they're just starting their design, they have my design as a reference and I'll stay with them and look at the designs as they come in and say, is it as good as mine?" he said.

"So really the only surprise is that it won one of the most prestigious awards in the world, you think to yourself wouldn't it be great to build that."

Landmark to 'rival Reichstag and Tate Modern'

It was announced last year a new fish market would be built around the corner from the existing one, and the more than $250 million price tag for the new development would be paid for by selling off the old site for high-rise apartments.

Mr Heenan said it would be a landmark development for Sydney.

"This Fish Markets in its new position will unlock nearly 7 kilometres of harbourside walkway, allow all of the peninsulas there, people living in those peninsulas, to drift down to the valleys and out to the water," he said.

"And in that journey it will come across nearly 3 hectares of extra public wharf area which has never been accessed by the public before at Blackwattle Bay, with 3,000 seats sitting around it and a market in one place, public square with temporary markets and dance and theatre performances, steps down to the water, boats, fishing boats, people coming in.

"It will feel like a public space, it will feel like an extension of Wentworth Park.

" I think that it's going to be so good that we'll call this the third most important green space in the city of Sydney.

"And all our figures are telling us that we'll get twice the numbers that visit the Reichstag, just because I've been in Berlin there last week, but equal to the Tate Modern numbers, so I think it's very exciting."