Over the weekend, a small fire was lit at the end of the jetty, wooden pillars were broken and the fence at its entrance was damaged.
The attack came just after the Governors Bay Jetty Restoration Trust bought the 150-year-old structure off the city council for $1 on Wednesday so it could take control of a $2.7m rebuild.
It has been closed since a post-earthquake engineering inspection in 2011 found it was unsafe.
Work will start in late February or early March, with the jetty expected to be reopened to the public late next year.
Trust secretary Louisa Eades said it was lucky the damage would not cause any setback.
She said there appeared to be two separate attacks – the fire was lit during the middle of the day on Saturday and the rest of the damage happened afterwards.
“The next thing we will do is make it as hard as possible for people to get onto the jetty, but it won’t delay anything.”
Deputy Mayor and councillor Andrew Turner, who officiated the sale last week, said he was shocked by the vandalism.
“It is particularly disappointing in view of the strong community support for the restoration of the jetty, the countless hours of volunteer time given by members of the trust and others, and the significant amount of funds raised from within the community for this project.”
“The Governors Bay community has been generous in so many ways which makes this act of vandalism particularly offensive. It is difficult to think of why anyone would have done this.”
The city council agreed to transfer ownership to the trust in 2016 so it could restore the jetty and has allocated $935,000 for the project in the Long Term Plan.
The trust is fundraising to pay for the remaining cost of the restoration.
Once it is fixed, the 150-year-old jetty will be sold back to the city council for $1.
