Corrosion, cracking and "significant defects" have been discovered in a privately owned concrete structure that supports a section of the Brisbane Riverwalk near Howard Smith Wharves.

The defects mean a concrete structure that carries large planter boxes at River Place Apartments, close to Boundary Street, have been emptied, after warnings the structure's load should be monitored closely.

Repairs are needed along a stretch of the Brisbane City Council-managed riverwalk under large planter boxes between the riverwalk and an apartment building behind it. Credit:Lucy Stone/Fairfax Media

A report commissioned by Brisbane City Council in October said the prestressed concrete plank structure, which also supports a section of the riverwalk, had "exceeded its service life" and needed "major intervention".

A council spokeswoman said the section of land the planter boxes were on was owned by the state government and leased to River Place Apartments.