Myanmar's parliament on Wednesday appointed the navy chief to replace a regime hardliner as one of the country's vice presidents, in a move seen as strengthening government reformers.

Admiral Nyan Tun, 58, who has a reputation as a political moderate, was selected by the military personnel who make up one quarter of the legislature and have the right to choose one of the two vice presidents.

"I will carry out my responsibilities honourably to the best of my ability and strive for the further development of the eternal principles of justice, liberty and equality," Nyan Tun said in his oath of office.

His appointment was approved by an electoral college, house speaker Khin Aung Myint announced at a joint session of the lower and upper houses of parliament in the capital Naypyidaw.

"He's very quiet and known as a flexible man," a military parliamentarian who did not want to be named said of the new vice president. "He has three children and lives a simple life."

His predecessor Tin Aung Myint Oo -- a renowned hardliner with close links to ex-junta chief Than Shwe -- resigned in July ostensibly due to ill health, fanning rumours of a power struggle between regime moderates and conservatives.

Since taking office last year, President Thein Sein, a former general, has overseen dramatic changes such as the release of hundreds of political prisoners and the election of opposition leader Aung San Suu Kyi to parliament.

The army's first candidate, Yangon chief minister Myint Swe, failed to win approval because his son-in-law is an Australian citizen, which under the constitution disqualified him from becoming a vice president.

"The Yangon chief minister is not qualified to be a vice president because of his Australian son-in-law. Military representatives changed the nomination in the last week of July to Admiral Nyan Tun," a parliamentary source told AFP.

The same provision is a barrier to Suu Kyi taking a top leadership role in the country, and her party has vowed to campaign to completely redraw the constitution, which was written by the former junta.

Myint Swe, a retired general, was one of the military leaders involved in a deadly crackdown on the "Saffron Revolution" monk-led uprising in 2007.