A National Party candidate says he is disturbed by the defacing of his election billboards with graffiti of Anzac poppies and crosses.

Dan Bidois, who is National's candidate in the Northcote byelection, said he discovered this morning that up to 10 of his billboards had been painted over.

"This isn't about the graffiti, the boards themselves can be replaced pretty quickly," he said.

"It's a bit disturbing and I hope others aren't too upset having to see this kind of thing because this can be an emotional day for many families.

"It's pretty disrespectful to do this on a day like Anzac Day. It's disrespectful to the men and woman that served, to their families and it's certainly disrespectful to the signs of Anzac."

Bidois, whose grandfather fought in World War II, said he could not understand the motivation behind the graffiti, which was limited to his billboards and not other candidates.

"But I haven't had time to speculate who or why they would have done this. All I can say is that it's disrespectful to the men and women that served."

The by-election was triggered by the resignation of National's former Health Minister Jonathan Coleman, who has held the seat since 2005.

Bidois, a former Fulbright scholar and ex-OECD economist is up against Labour's Shanan Halbert, a former Maori TV presenter who now works at Te Wananga o Aotearoa.

The Greens will also be standing a candidate, while NZ First is yet to decide whether it will run.