Naming rights at a range of prices are on offer for as many as 10 spaces in the iconic gallery, with the premier spaces available for up to $1 million.
"We believe there are family trusts, corporate, businesses and individuals who will see the value in creating a legacy within a complex that will put Whanganui on the map as a leading centre for culture and the arts," she said.
"We have fought very hard and have come too far to fail at the final hurdle."
The major restoration will ensure the preservation and seismic strengthening of the gallery, which is one of New Zealand's oldest purpose-built galleries.
It will then be able to properly store and display its nationally significant collection of more than 8000 works spanning 400 years of international and New Zealand art history.
The project includes earthquake strengthening and restoration of the existing historic building and construction of a new purpose-built wing with storage, education, exhibition and retail spaces.
Developed design drawings have been prepared by Warren and Mahoney Architects and once funds are in place detailed designs will be drawn up with construction due to get under way in late 2018 or early 2019.
With the December deadline looming, Ms Williams saisd all contributions, large and small, would make a difference.
There is currently a Thousand Stars initiative through which people make weekly contributions of $5 over a four year period. Contributors can vary the amount and frequency of payments on a monthly, quarterly or annual basis, and more than 350 people have signed up to the initiative.
Businesses are also being encouraged to sign up to the Sarjeant Gallery Business Initiative with the option of making a one-off payment of $5000, regular quarterly payments of $630 over two years or monthly payments of $210 for two years.
The gallery was founded with a bequest from Whanganui resident Henry Sarjeant in 1912 and built in 1919 on its Queen's Park site overlooking Whanganui. It is listed as a category 1 heritage building by the Historic Places Trust.
The collection includes old master and contemporary paintings as well as works by Colin McCahon, Ralph Hotere, Pat Hanly, Charles Frederick Goldie, Gottfried Lindauer and Petrus Van Der Velden.
The collections also include New Zealand and international sculptures, pottery, ceramics and glass, bronze works and video art and the largest photographic collection outside of Auckland and Wellington. The collection was valued at $28.8 million in 2017.
At a glance:
+The project is a partnership between Whanganui District
Council, Whanganui Iwi, central government, large and small
donors and sponsors
+The re-development will double the size of the existing
facility
+A new purpose-built wing to the north of the existing gallery
will honour the memory of Sir Archie Te Atawhai Taiaroa.
+The total estimated cost of the project is $34.9 million, with
the district council contributing $5 million
+Approximately $11.8 million has been donated in cash and
pledges by community, private trusts and individuals -
conditional on targets being met.
+$10 million from the Regional Culture and Heritage Fund was
granted in 2016 subject to the Sarjeant Gallery Trust raising
outstanding funding by December 2017.
+As part of the conditions, Whanganui District Council is
required to agree to underwrite any cost over-runs and/or
cover any shortfall in funds raised.
+The remaining shortfall of approximately $2.2 million will
consist of approaches to private trusts and private individuals.