A new park at Brisbane's busy riverfront South Bank precinct could take at least another year to complete and is set to cost taxpayers millions of dollars more than expected because of a redesign.

Key points: South Bank Corporation says the park was delayed by a change in the plans

South Bank Corporation says the park was delayed by a change in the plans It says enhancements include added rainforest and a new connection to the river

It says enhancements include added rainforest and a new connection to the river It is now expected to be completed by the end of 2020

The State Government originally wanted the site to be developed into open parkland by removing a restaurant complex that had been abandoned after the 2011 floods.

But construction of the new park has only just begun, with figures in this year's budget revealing it will cost $18.5 million — almost $3 million more than initially planned.

Former infrastructure and planning minister Jackie Trad first announced plans two years ago, saying she expected the land to be returfed and redeveloped by the end of 2017.

Then the new Infrastructure and Planning Minister Cameron Dick said in March 2018 that construction on the riverfront park would begin "mid-year".

Construction underway at the South Bank park site yesterday. ( ABC News: Josh Bavas )

The old restaurant building was demolished in 2018, but construction on the new park only began last month, after South Bank Corporation awarded tenders.

The park's final designs have been provided to ABC News, showing how the 6,800-square-metre site will be repurposed to include a new rainforest extension and pavilion area.

A spokeswoman for South Bank Corporation said the delay was due to a change in the plans, which now included "added enhancements" to the promenade.

South Bank Corporation now says the project won't be complete until the end of 2020. ( Supplied )

"Visitors to South Bank will be able to experience stunning city views, lush rainforest and a new connection to the river as a result of this urban redevelopment project," she said.

The spokeswoman said the park was likely to be ready for public use within 18 months.

"South Bank Corporation expects the project to be complete by the end of 2020," she said.

As well as open park, the new zone will include a rainforest extension and a pavilion. ( Supplied: South Bank Corporation )

"As Brisbane's population grows, South Bank is evolving to meet the emerging needs of the community for more green space, which is what this project delivers."

Opposition Leader Deb Frecklington said she could not understand why the project was taking so long.

"What we need to see is a bit more substance over spin," she said.

The old restaurant complex was demolished about a year ago. ( ABC News: Josh Bavas )

"What we've seen is two announcements and this parkland still not coming up out of the ground — what is the delay?"

Mr Dick declined to comment on the project's timing.

While Brisbane City Council is contracted to maintain the parklands, South Bank Corporation remains responsible for overall management of the precinct, including the commercial assets, retail tenancies and renewal projects.