OTTAWA (Reuters) - Canadian Prime Minister Justin Trudeau faced fresh questions about his political future on Tuesday after the ruling Liberal Party lost a safe seat in a special election, underlining his unpopularity.

Final results, released at about 5 am (1000 GMT), showed the official opposition Conservatives had won the race in the Toronto-St Paul's constituency for first time since 1988. The election was called after the previous legislator quit.

The victory marked the first time since 2015 that the Conservatives had broken the Liberals' control of vote-rich Toronto, which is home to dozens of seats and key to Trudeau's hold on power.

"What a disaster for the Liberals," said Philippe Fournier, editor in chief of the 338Canada website, which models electoral projections across the country.

The next federal election must be held by October 2025 and a range of polls show the Liberals, who have been in power since November 2015, would lose badly to the Conservatives.

The loss indicates Liberals in less safe Toronto area seats might be vulnerable, underlining the challenge for Trudeau.

Some political commentators have mused that the Liberals might do better if they moved on from Trudeau, who has so far insisted he will fight the next election.

"Canadians are not in a decision mode right now," he told the Canadian Broadcasting Corp last week.

Names of potential leadership candidates include former Bank of Canada governor Mark Carney and Public Safety Minister Dominic LeBlanc, a close Trudeau friend.

But unlike Britain and Australia, where the prime minister is elected by legislators and can be removed relatively easily, party leaders in Canada are chosen by special conventions which are held on fixed dates. It is therefore almost impossible to ditch a leader who does not want to leave.

Governments who have been in power for several years tend to do badly in special elections, which they usually attribute to low turnout and voters wishing to send a protest message.

But Darrell Bricker, CEO of Ipsos Public Affairs, noted that a relatively high 44% of voters had cast a ballot.

"This was a workday Monday in a riding that is a Toronto traffic nightmare. This shows a strong desire among voters to send a signal for change," he said in a social media post.

The Conservatives say they have four priorities: axing a carbon tax introduced by the Liberals, addressing the government's budget deficit, tackling a housing crisis and cracking down on crime.

The Liberal candidate was Leslie Church, former chief of staff to Finance Minister Chrystia Freeland and a member of Trudeau's inner circle.

Despite a high profile campaign boosted by the visit of several top cabinet members, she won only 40.5% of the vote compared to 42.1% for the Conservative candidate. In the 2021 election, the Liberals won by 49% to 22%.

Trudeau's office was not immediately available for comment. His schedule for Tuesday did not show any media availabilities.

(Reporting by David Ljunggren; Editing by Alistair Bell)

By David Ljunggren