Thieves who stole thousands of dollars worth of solar panels and batteries from a Whangarei Harbour navigation light possibly went back a few days later to rip off the remaining gear.
The second hit on Northport's 14-metre high Tamaterau Port Entry Light near Onerahi was discovered on Tuesday this week when staff went to install a stop-gap fix after the first theft at least a week earlier.
Deputy Harbourmaster Tony Browne described the thieves' disregard for public safety as "disappointing and selfish".
The light is an important navigation aid used by large commercial ships heading to and from Portland and Whangarei, he said.
While the Tamaterau light was the most vital, thieves had also stolen equipment from a much smaller Northport navigation aid on the western side of One Tree Point.
Six 200-watt solar panels and brackets, a wind generator and post and a number of batteries collectively worth several thousand dollars were stolen altogether.
Then the thieves apparently returned to steal electrical control equipment from the Tamaterau pole that they had been unable to remove the previous time.
The temporary-fix plan would have required all ships using the upper harbour that needed the light to radio ahead so it could be turned on.
Damage at the site means even the temporary solution, that would have delivered limited power to the light, is no longer possible.
Northport estimated it could take a number of weeks to obtain and manufacture the necessary parts to repair the light.
In the meantime, a new navigation safety warning for the area has now been issued advising the light is still inoperable and urging ships to navigate with caution.
Mr Browne said the white light ahead lets ship captains know they are in the right place in the channel, but shows a green light or red if the ship veers to port or starboard.
The thefts have been reported to police and Mr Browne reiterated earlier statements that officials take an extremely dim view of the thieves' actions.