Toronto Mayor Rob Ford, who gained global notoriety last year for admitting he smoked crack cocaine, has dropped out of the race for re-election as mayor on Friday after he was diagnosed with an abdominal tumor this week.

A city clerk told reporters that Rob Ford's nomination had been withdrawn just ahead of a deadline for ballot changes to the Oct. 27 election.

Speculation remains that Ford's elder brother, Doug Ford, could replace him on the mayoral ballot. The mayor's nephew Michael Ford also withdrew his nomination for election to city council. That may clear the way for Rob Ford to run for city council instead in that district.

Ford Thursday transferred hospitals via ambulance to a facility specializing in cancer treatment, a day after initial tests uncovered a tumour in his abdomen.

The city's Humber River Hospital announced in a statement that Ford had been moved to Toronto's Mount Sinai "for follow-up investigation and subsequent treatment."

The 45-year-old mayor only returned to work in June after two months in rehab for drug and alcohol abuse, including the use of crack cocaine while in office.

He sought medical help after complaining of abdominal pains that had persisted for more than three months but suddenly became worse from Tuesday to Wednesday.

A CT scan revealed a tumor in his abdomen but the Ford family was still awaiting biopsy results that would determine the type, and whether it is malignant or benign, his doctor Rueben Devlin said.