The Historic Places Trust has received a large anonymous donation towards the repair of the earthquake-damaged Timeball Station in Lyttelton.
The 136-year-old heritage building partially collapsed during the Canterbury earthquakes and is one of a handful of similar buildings left in the world.
Between 1876 and 1934, a large ball dropped from the mast on Timeball Station's stone tower, signalling the time of day to ships in Lyttelton Harbour.
Paul McGahan, the trust's heritage destinations southern regional manager, would not say how much money has been donated - only that it is a very significant figure.
Mr McGahan says the trust is proposing to build a replica of the tower on the site using new and original materials.
A recent geotechnical report found that the land underneath the station is safe to be rebuilt on.