The Department of Conservation is planning to replace the swing bridge on the walking track leading to the Rob Roy glacier in the Mt Aspiring National Park.
The bridge, across the west branch of the Matukituki River, was constructed in 1978 and is used by about 20,000 people each year.
A DoC spokeswoman said the existing bridge was considered to be nearing the end of its useful life and building a new $50,000 bridge had been recommended by a DoC structural engineer.
The existing bridge would be closed to the public from April 2-23 while the replacement was built.
The work would be done by DoC staff along with an earthmoving contractor. A helicopter would be used to fly concrete in and to assist with building the towers at each end.
The bridge would be on the same site but would be wider and its maximum loading would double, to 10 people.
The spokeswoman said construction was being undertaken after the Easter holidays to limit disruption.