Sydney needs to get high, according to a property developers' lobby group that says the city's skyscrapers must double in height by 2050.

Citing PricewaterhouseCoopers research that shows Melbourne and Brisbane both outstripping the harbour city’s economic growth, the Urban Taskforce said authorities must scrap existing building height limits and allow Sydney to grow skywards.

“For Sydney to remain as Australia’s number one city we need to plan for doubling the height of our skyscrapers by 2050,” said Chris Johnson, CEO of the Urban Taskforce.

“Sydney is being held back by out-of-date planning rules that set the underside of Sydney Tower, designed in the 1970s, as the cap on height for new buildings.

“Across Asia, many cities are building towers that are symbols of the prosperity and the optimism of that city’s economic growth.”

The Urban Taskforce commissioned three architects to envision what Sydney might look like by 2050.

One ambitious image, produced by Philip Vivian of architectural firm Bates Smart, shows Sydney full of skyscrapers and looking far more like Hong Kong than the harbour city of today.

Mr Vivian’s vision also included a metro system that crosses the Harbour Bridge.

That might seem like pie in the sky for a city already struggling with far more basic issues, such as keeping up existing public transport demand and road building.

But Mr Johnson said he wanted to contribute to the debate about Sydney’s future.

“The Urban Taskforce urges Sydneysiders to think big for Sydney’s future so that we keep ahead of Melbourne and Brisbane as they push forward,” he added.

“Even more important is that Sydney is positioned in the Asia Pacific region as one of the leading cities along with Shanghai, Hong Kong and Singapore.”