Larry O'Brien told a crowd in the Byward Market on Wednesday his work as Ottawa mayor isn't finished yet, while at a rally in south Ottawa Jim Watson assailed O'Brien's first term in office. (CBC)

Larry O'Brien kicked off his campaign for re-election on Wednesday, saying his work as Ottawa mayor "isn't finished yet," while at a rally in the city's south end, rival Jim Watson took aim at what he called "four, long, frustrating years" under O'Brien.

Ottawa's mayoral race got off to an early start on Tuesday when Watson and fellow mayoral hopeful Councillor Clive Doucet launched parts of their platforms. But for the O'Brien campaign, Wednesday night's rally in Ottawa's Byward Market marked the official launch of his bid for re-election.

O'Brien, who made plans for a light rail transit system a focus of his first term, called on voters to give him another mandate to work to fix Ottawa's roads and shake-up OC Transpo.

O'Brien said if re-elected he would work to establish an arms-length transit commission, like Toronto's, to take the business of running the service off council's plate.

"The days of council debating bus routes and union contracts must end," said O'Brien. "It's time to put the management of this asset in the hands of professionals."

O'Brien's pledge in the last election of "Zero means zero" has been the primary ammunition against him after taxes increased 14 per cent during his first term.

But surprisingly, O'Brien returned to that familiar promise, pledging to attempt zero tax increases and scoffing at Watson's pledge to cap annual tax increases at two and a half per cent.

"This mayor will never give up on the goal of zero tax raises!"

O'Brien said he admits the goal is impossible without a like-minded council and urged residents to vote one in.

"The mayor may only have one vote, but you my friends have two, one for mayor and one for councillor. Make both votes count!" he said.

Watson dismisses the mayor's tax pledges

Watson, who launched his campaign at a rally at Tudor Hall in Ottawa's south end, focused much of his speech on O'Brien's record, describing the mayor's four-year term as "chaos" and saying the mayor's latest pledge on taxes cannot be taken seriously.

"After four long and frustrating years, welcome to the only mayoralty campaign to bring real change to city hall," said Watson.

Aside from attacking the mayor's record and reiterating his pledge to cap tax increases, Watson outlined only one major new platform position, a promise to build an east-west transit line on time and on budget.

Both candidates referenced future campaign announcements, with O'Brien saying he will outline a plan to "take control" of salaries at city hall when he unveils his economic platform on Sunday, while Watson said he'll focus his next announcements on plans for environment, housing and tourism.

The municipal election will be held on Oct. 25.