Papakura Coastguard officials responding to a boatie in trouble arrived at work to discover vandals had smashed up an emergency response vehicle.
Vandals smashed a window and tore a door handle off an emergency response vehicle belonging to Papakura Coastguard.
Police are investigating the break-in.
The charity said it received a callout on Saturday at 1am to assist a boat with engine trouble.
"Unfortunately, arriving at base, we were pretty shocked and disappointed to see that someone had broken the window of our pool car and ripped the handle off our truck," the organisation said on Facebook.
"These are emergency response vehicles with nothing of value stored in them. Sad that people feel the need to break into them."
Despite the setback, the callout was successful and the boat in trouble was towed back to shore.
"Thankfully, the truck was still usable for the callout and we were able to take a private vehicle as well," it added.
The damage was described by the charity as "significant" and there are fears that money raised at its annual garage sale on March 23 will have to be spent on repairing the vehicles.
Its Facebook post has received 350 reactions, 85 comments and shared 106 times as at 9am Sunday morning, and sentiments are running high.
"That's sad that people feel the need to vandalise other people's property, especially that used for saving people's lives. Let's hope they see this post and realise what losers they are," Marilyn Retter wrote.
"CG [Coastguard] does such an awesome job, and don't deserve this added stress. Must be heart wrenching for volunteers to find themselves in situations like this one."
Another poster, Sam Sword, said: "This is shocking, do people not realise that 1 stupid action can put the life of others at risk!"
• Anyone with information can call Papakura police on 09 295 0200.