More than two decades after its stolen election win, Aung San Suu Kyi's opposition party is set for a dramatic political comeback in Myanmar polls which could herald an easing of sanctions.

The Nobel laureate, who spent most of the past 22 years locked up by the generals, is widely expected to win a seat in a parliament dominated by the military and its political allies in by-elections to be held on Sunday.

Victory for the former political prisoner would cap a remarkable transformation for the 66-year-old icon of the pro-democracy movement.

Her National League for Democracy (NLD) party will contest 44 of the 45 seats available in Sunday's vote, alongside the army-backed ruling Union Solidarity and Development Party and other opposition parties.

But the world's eyes will be on the dusty constituency of Kawhmu near Yangon where the daughter of Myanmar's independence hero General Aung San is standing for a seat in parliament for the first time.

While the number of seats at stake is not enough to threaten the ruling party's overwhelming majority in parliament, a win would give Suu Kyi a chance to influence the legislative process for the first time.

"Her transformation in recent months is striking," said Renaud Egreteau, a Myanmar expert at the University of Hong Kong.

"She is in the full spotlight today and is savouring it with ceaseless campaigning and meetings -- at the cost of her health."

Suu Kyi is showing signs of strain. She cancelled campaigning this week after she fell ill and was put on a drip following a gruelling schedule of rallies and speeches across the country.

Huge crowds of supporters have turned out to see her on the campaign trail, and meeting their high expectations for change in the impoverished country after years of repression and isolation will be no easy task.

"We think she can make everything happen, more than anyone else," said NLD supporter Ashin Munida who attended a recent rally. "We have big expectations of her," he said.

After almost half a century of iron-fisted military rule, the junta in March last year handed power to a new government led by President Thein Sein, one of a clutch of former generals who shed their uniforms to contest a 2010 election.

That vote, won by the military's political proxies, was marred by widespread complaints of cheating and the exclusion of Suu Kyi, who was released from seven straight years of house arrest shortly afterwards.

Since then, however, the reform-minded regime has released hundreds of political prisoners and held a dialogue with Suu Kyi, whose party won a landslide election victory in 1990 but was never allowed to take office.

In the run up to this Sunday's by-elections, the NLD complained about apparent irregularities, notably the appearance of the names of some dead people on the electoral roll.

Thein Sein acknowledged in a recent speech that there had been "unnecessary errors" in ballot lists, but said that the authorities were trying to ensure the by-elections will be "free and fair".

"Winners and losers will emerge in the by-elections as per usual. We all need to work together to ensure that the outcome is accepted by all the people," he said.

Unlike in 2010, the government has invited foreign observers and journalists to witness a vote seen as a major test of its reform credentials.

The European Union, United States and other Western nations this year started easing some sanctions on Myanmar in recognition of its recent positive moves towards political reform after decades of direct military rule.

While a successful vote could encourage further steps by the West, concerns remain about the continued existence of political prisoners and alleged rights abuses by the military, particularly in ethnic conflict zones.

Nevertheless, experts believe the regime wants the pro-democracy leader to win a place in parliament to burnish its reform credentials.

"Of course they need Aung San Suu Kyi to get legitimacy. The military government is strong in every way but in terms of legitimacy they are very weak," said Toe Zaw Latt, Thailand bureau chief of the Democratic Voice of Burma, an Oslo-based broadcaster that was banned under the junta.

"It is a critical moment for the government about their sincerity and their intention to reform," he said.