Canadians are casting votes in a general election with opinion polls pointing to a likely Conservative win for the first time in 12 years.
Opinion polls favour Mr Harper (L) over Mr Martin
The second election in 18 months was triggered when Liberal Prime Minister Paul Martin lost a confidence vote.
Conservative leader Stephen Harper has pledged to cut taxes and tackle violent crime and corruption.
Polling stations in Newfoundland were first to open as the election unfolded across Canada's six time zones.
The weather across most of the country was mild and officials in the east said turnout was brisk, according to Reuters news agency.
Two last-minute opinion suggested the Conservatives would be 10 points ahead of the Liberals - at 37% to 27% - but they also indicated the party would not secure an outright majority in the 308-seat house.
Correspondents say that the Canadian economy is buoyant, but the Liberals have been hurt by accusations of corruption.
Voters in 60,000 polling stations are choosing from parties including the Greens, the left-wing New Democratic Party and French-speaking separatist Bloc Quebecois.
The last stations will close at 0300 GMT on Tuesday on the Pacific coast, but an indication of the outcome should emerge before then as voting will have already ended in the key provinces of Ontario and Quebec.
The Liberals have been focusing on economic successes, pointing to eight consecutive budget surpluses.
Mr Martin said on Monday that he was confident of victory.
The Bloc Quebecois' Gilles Duceppe makes a final plea to voters
"It's certainly a close one, but I've got to say I feel pretty good," he told Vancouver radio station CKNW.
But the BBC's Lee Carter in Toronto says the corruption scandals that have beset the Liberals in recent years seem to be sticking this time.
The confidence vote was triggered by a public inquiry that found Liberal politicians in Quebec had taken kickbacks in return for government contracts.
Mr Harper's critics say he will destroy social programmes and has extremist views.
However, in contrast to the last election, he has promised Canadians that he will not move the country too far to the right if he is given a mandate.
The momentum appears to be against Mr Martin, our correspondent says, after four consecutive Liberal governments.
Opinion polls even suggest the Conservatives will make inroads in Quebec, a part of the country they have been frozen out of for more than a decade and where separatists had been expected again to make a clean sweep.
*Increased to 15 seats in 2002 after two by-elections and the admission of a Democratic MP
**Reduced to 98 after defection of an MP
Total seats in Canadian Parliament: 308