"I am aware that it is difficult for organisers of events at this stage of the campaign," he said.
"Hard calls have to be made about efficient use of time and reaching the largest number of voters as time runs out."
Collins later posted a picture to Twitter of him at an event in Otara, writing: "Added to this special evening is my daughter is performing siva Samoa with all her friends. My heart is filled with pride and excitement."
A spokesperson for Collins' rival, Wayne Brown, said "if one of the two major candidates pulls out then there can't really be a debate."
Brown also pulled out of the event.
Brown's spokesperson said, "Wayne was notified this afternoon that Efeso had pulled out of the debate, his fifth no-show this week at scheduled events."
Collins also pulled out of a debate to be hosted by NZ Punjabi News last night, as well as a meet-the-candidate event co-hosted by the Milford Residents Association.
The string of cancellations comes as Wayne Brown pulled ahead of Collins in the latest Ratepayer's Alliance-Curia poll. Brown leads with 28 per cent, with Collins trailing at 26 per cent.
Brown's ratings rose 8 percentage points since the last poll.
Collins previously criticised Brown for pulling out of the Herald's mayoral debate last Friday.
He called Brown's pulling out an "insult to Aucklanders".
Collins said Aucklanders "deserve better than a candidate trying to run a campaign via a few flashy billboards in just a handful of suburbs while avoiding engaging with voters across our city by missing a key event run by one of Auckland's main media outlets".
Brown pulled out of a debate due to his belief the debate's host, Simon Wilson, could not be seen as "neutral or independent".
But regarding his cancellation of Thursday evening's debate, Collins said: "Unlike my opponent Wayne Brown, I have never cancelled events because I have a problem with the audience or moderator.
"I would have loved to attend the event this evening but - after trying to accommodate both events - I was left with no other choice but to withdraw."
Tonight's debate was to be hosted at the PwC Tower by the Commercial Bay Club, a group for employees of some central city businesses.
Rival candidate Craig Lord, polling in a distant fourth place on 4 per cent in the Alliance-Curia poll, took to social media to voice his disappointment that the debate was cancelled.
Lord said: "Wow. Guess who just pulled out of another mayoral debate. I've lost count how many times this has happened."
"[This is] severe disrespect towards the voters and organisers," he said.
Lord was supposed to participate in the evening's debate.
