Voting began on Sunday in Myanmar's first free nationwide election in 25 years, the Southeast Asian nation's biggest stride yet in a journey to democracy from dictatorship.

The party of opposition leader Aung San Suu Kyi is expected to win the largest share of votes cast by an electorate of about 30 million, who will choose from among thousands of candidates standing for parliament and regional assemblies.

But a legacy of military rule means she cannot become president after the election, even if her National League for Democracy (NLD) wins a landslide, and many voters voiced doubts that the generals would accept the result.

There has been concern about the fairness of the election after it emerged that about 4 million people will be unable to cast a ballot, and on the eve of the poll the NLD said a suspiciously large number of extra voting tickets had been issued in some areas, with one family in Yangon getting 38.

Religious tensions, fanned by Buddhist nationalists whose actions have intimidated Myanmar's Muslim minority, also marred the election campaign.

Still, there was a palpable sense of excitement among voters as they went to polling stations, many before dawn.

"I've done my bit for change, for the emergence of democracy," said 55-year-old former teacher Daw Myint after casting her vote for the NLD in Yangon. "I do hope everything goes well in this historic event."

Suu Kyi's car inched through a scrum of news photographers outside the Yangon polling station where the 70-year-old Nobel peace laureate came to vote and she was stony-faced as bodyguards shouted at people to move aside.

Most in the crowd of well-wishers gathered there were lucky to get a glimpse of the garland on her hair as she went inside, without a smile or a wave, to cast her vote.

Khin May Oo, 73, voting at the same polling station, said he believed the country was at a turning point, but he was worried about the army: "I'm not sure whether they will accept the election results," he said.

"VERY SILLY" CONSTITUTION

Results from the one-day election are expected to come in slowly: officials say the winners of a few parliamentary seats will be announced by the end of Sunday, but a clear overall picture is not expected until Monday evening at the earliest.

Suu Kyi won the last free vote in 1990, but the military ignored the result. She spent most of the next 20 years under house arrest before her release in 2010.

She is barred from taking the presidency herself under a constitution written by the junta to preserve its power.

But if she wins a majority and is able to form Myanmar's first democratically elected government since the early 1960s, Suu Kyi says she will be the power behind the new president regardless of a constitution she has derided as "very silly".

Suu Kyi starts the contest with a sizeable handicap in parliament: even if the vote is deemed free and fair, one-quarter of parliament's seats will still be held by unelected military officers.

To form a government and choose its own president, the NLD on its own or with allies must win more than two-thirds of all seats up for grabs. By contrast, the ruling Union Solidarity and Development Party (USDP) would need far fewer seats if it secured the backing of the military bloc in parliament.

However, many voters are expected to spurn the USDP, created by the former junta and led by former military officers, because it is associated with the brutal dictatorship that installed President Thein Sein's nominally civilian government in 2011.

An inconclusive result could thrust parties representing Myanmar's myriad ethnic minorities into a king-maker role, bringing them closer to the center of power after years on the fringes.

MILITARY POWER

Even if the NLD is victorious, the military will retain significant power. It is guaranteed key ministerial positions, including defense, interior and border security, and the constitution gives it the right to take over the government under certain circumstances. It also has a grip on the economy through holding companies.

Until just a few years ago a pariah state, Myanmar had little experience organizing elections.

In a pre-election speech on Friday, President Thein Sein acknowledged that organizing the vote was a challenge and stressed the government's commitment to ensuring a credible vote, with more than 10,000 observers scrutinizing the process.

Security was tight around the country, with 40,000 specially trained police watching over polling stations, and many restaurants and markets closed in the country's usually bustling main city, Yangon.

Wa Gyi, owner of a roadside food stall in Yangon, said he had been ordered to close for the day. "It's OK for us," he said. "It's our contribution to the emergence of democracy."