He said Ford had been suffering from stomach pains for at least three months and they had worsened in the last 24 hours.

"It became unbearable for him," he said.

Ford, 45, acknowledged smoking crack cocaine while in a "drunken stupor" following months of denials. The mayor returned to work in June after a rehab stint for drug and alcohol abuse and is running for re-election on October 27.

Devlin said they need to determine what type of tumour it was by doing a biopsy. He said he could not say how long Ford would be in the hospital.

Devlin said the CT scan was "very definitive for the tumour" but a "definitive diagnosis" is still to come.

Ford had previously said he had abdominal surgery to remove a tumour on his appendix. "I had a major surgery on my appendix; they took out a piece of my colon. So I had a tumour in my appendix, and that's pretty scary when that happens," he told CTV television in 2010.

Doug Ford Senior, the mayor's father, died of colon cancer in 2006.

Councillor Doug Ford, the mayor's brother and campaign manager, said Ford was in good spirits.

Doug Ford was visibly shaken as he sidestepped questions about the mayoral race and whether his brother would drop out of the race. Although campaigning has been under way for months, the official deadline for candidates to sign up is today. That leaves time for Doug Ford to step in for his brother, a possibility some have long speculated about.

Doug Ford said his brother complained of stomach pain over breakfast together.

"He said his stomach was bothering him. He went to the doctor's and the doctor sent him over to Humber," Doug Ford said.

Dennis Morris, the mayor's lawyer and a family friend, said he spoke to Ford on Tuesday and he didn't mention any abdominal pain. Ford appeared well during a debate on Tuesday night.

The mayor has steadfastly refused to step down since reports emerged of a video of him smoking crack.

Ford, who came to power pledging to cut waste at city hall and keep a lid on taxes, has a core base of suburban support in Canada's largest city. But he has trailed in the polls ahead of the election. A new poll published on Wednesday showed Ford running second behind former businessman John Tory, with 28 per cent support compared with 40 per cent for Tory.

Left-leaning Hong Kong-born candidate Olivia Chow was in third place in the three-way race.

"My thoughts and hopes are with @TOMayorFord and his family for good news in the days ahead," Chow tweeted on Wednesday night.

Tory also sent a message of support to his political rival, saying he wanted Ford "back where he would want to be - with us at the debating tables talking about the city we all love".

This article appeared in the South China Morning Post print edition as: Hospital admits Rob Ford for tumour