Burma's opposition leader Aung San Suu Kyi has said she will be the true power above the country's president if her party wins historic elections this Sunday.

"It's a very simple message," Ms Suu Kyi said, when reporters pressed her to explain what she meant. While another member of her National League for Democracy party would hold the presidential title, "I'll make all the proper and important decisions."

A constitutional clause bars Ms Suu Kyi from the top job.

"I'll be above the president," she said, appearing bemused as she spoke to hundreds of reporters gathered at the lakeside villa that was her prison before the country began its transition from dictatorship to democracy five years ago. "I'll run the government."

She insisted her plan was legal because "the constitution says nothing about being 'above the president'".

Although the comments run contrary to democratic norms, which Ms Suu Kyi has always stood for, they represent the reality in Burma's present ruling structure.

The current president takes instructions from the military-backed Union Solidarity and Development Party and if a military person were to become president, he would be beholden to the army commander.

Sunday's elections are billed as Burma's best chance ever for a free and credible vote, with experts noting the nation experienced widespread suppression of dissent and violence even before the 1962 coup that plunged the country into military rule for the next half-century.

But the constitution, drafted under military control, guarantees that the armed forces maintain control more than 25 per cent of the seats in parliament and the key security portfolios.

In a clause widely seen as custom-tailored for Ms Suu Kyi, it also bars her from the presidency because her late husband was British and her two sons hold foreign passports.

The 70-year-old opposition leader said the run-up to the vote had been seriously flawed and that she hoped the international community would not be too quick after ballots were counted to declare it free and fair, noting the US and others have at times been overly enthusiastic about political and economic reforms.

"I ask them," she said, beyond the veneer, "what has changed?"

The Union Election Commission, which oversees the voting, is headed by a vocal supporter of President Thein Sein's ruling Union Solidarity and Development Party.

Ms Suu Kyi said the commission had ignored repeated complaints about irregularities in advance voting, the illegal use of religion by her political opponents, and the disenfranchisement of migrant workers.

She did not mention the country's 1.3 million Rohingya Muslims, who have been denied the right to vote for the first time since independence.

The government says all are illegal migrants from neighbouring Bangladesh, though many of their families arrived generations ago.