The mayor of Canada’s largest city Toronto has admitted that he once smoked crack, months after a video allegedly showing him taking the drug surfaced, rejecting calls for his resignation.

Rob Ford, 44, however, denies he is an addict, in comments that marked a stunning turnaround following months of steadfast denials of the explosive drug allegations and has made a bid for re-election.

“Yes, I have smoked crack cocaine,” Ford told reporters outside his office on Tuesday.

“Am I an addict? No. Have I tried it? Probably in one of my drunken stupors,” he added.

Ford says he believes the incident happened “about a year ago”, but admitted: “I don’t know exactly.”

This is absolutely tragic. Tragic. Nobody can or should take any joy in this. #TOpoli #Toronto

— Cdn Politico (@CdnPolitico) November 5, 2013

In a press conference Ford refused to resign, and promised not to repeat his behaviour.

“I want to be clear, I want to be crystal clear to every single person. These mistakes will never, ever, ever happen again.”

Ford said he was embarassed and ashamed of his behaviour, which he kept a secret from family and friends.

Lots have people have urged @TOmayorford to seek rehab and step aside. Clearly he is not listening. Makes announcement and walks. #TOpoli

— Rob Ferguson (@robferguson1) November 5, 2013

“To the residents of Toronto, I know I have let you down. And I can’t do anything else but apologise,” he said.

“I’m so sorry. I know – I know, I have to regain your trust and your confidence. I love my job. I love my job. I love this city. I love saving the taxpayers money and I love being your mayor. There is important work that we must advance and important decisions that must be made.”

Did you hear the laughter when #RobFord ended with "God Bless Toronto." > Wowzas.

— Asha Tomlinson (@AshaTomlinson) November 5, 2013

The 90-second clip at the centre of the scandal has caused an uproar since its existence was first reported in May.

The daily Toronto Star and American gossip website Gawker said they had seen the footage, which reportedly showed a man resembling Ford lolling back in a chair in a room, inhaling from what appeared to be a glass crack pipe.

But after Gawker raised more than $US200,000 ($A210,700) in an online campaign to buy the video, it said it was told by its unnamed source that the video was “gone”.

Last Thursday, Toronto police chief Bill Blair said technicians had salvaged the deleted video and other data from a hard drive seized in an investigation of the mayor’s longtime friend Alexander Lisi for extortion, related to Lisi’s attempts to recover the video.

Ford has since apologised for “mistakes” but had until Tuesday steadfastly denied the drug allegations, rebuffed calls for his resignation and vowed to run for re-election next year.

This picture just confirms there's a Simpsons moment for everything. #robford #toronto pic.twitter.com/LuLjh9mXhL

— Matthew Kang (@MatthewKangCBC) November 5, 2013

He and his lawyer, meanwhile, have called on police to release the video, but Blair declined, saying it was evidence in a criminal case now before the courts.