Access to New Zealand's tallest surviving kauri tree, Tāne Mahuta, will be closed for the next two months while the boardwalk and viewing platform are replaced.

The upgrade is the first phase of a project by the Department of Conservation (DOC) and Te Roroa iwi to improve visitor infrastructure in Northland's Waipoua Forest.

The work also aims to protect the forest from the spread of kauri dieback, a deadly pathogen already present at Waipoua.

DOC Kauri Coast manager Stephen Soole said facilities at Tāne Mahuta were no longer fit for purpose and put the forest and its 200,000 visitors per year at risk.

Work by Milton Harward Construction would start on 30 September, and was due to be completed by the end of November in time for the busy summer season.

Other walks in Waipoua Forest, including to another immense kauri, Te Matua Ngahere, remained open in the meantime.

The new walkway was part of the wider Rākau Rangatira project to upgrade infrastructure and improve the visitor experience in Waipoua Forest, while prioritising forest health.

Future initiatives could include guided walks and a park-and-ride option.

If introduced, Soole said they could "deepen visitors' connection to culture and nature, increase public safety, minimise environmental impact, and allow visitors to play an active role in contributing to ongoing conservation".

Improved infrastructure could allow visitors to experience previously inaccessible areas, such as a wetland behind Te Matua Ngahere.

Tāne Mahuta, 51.5m tall with a trunk diameter of 4.5m, was estimated to be 1500 years old.

Kauri dieback was caused by Phytophthora agathidicida, a soil-borne pathogen that infected kauri trees through their roots.

It restricted the ability of kauri to transport water and nutrients between their roots and leaves, eventually causing the trees to starve.

Kauri dieback had so far been found in Northland, Great Barrier Island, and Coromandel Peninsula.