Secretary of State Hillary Clinton headed to Myanmar Wednesday in the first top-level US visit for half a century, hoping to ignite a "movement for change" in one of the world's most closed nations.

After attending an aid conference in South Korea, Clinton was flying to a little-used airport in Naypyidaw, Myanmar's remote showcase capital unveiled in 2005 by military rulers of the strategic but long-isolated country.

Myanmar, formerly known as Burma, has surprised observers with a series of reformist moves in the past year, including releasing opposition leader Aung San Suu Kyi from house arrest and nominally ending decades of military rule.

President Barack Obama personally announced Clinton's trip during a visit to Asia earlier this month, citing "flickers" of hope. But his administration has sought to keep expectations low, mindful of other false dawns in Myanmar.

Just prior to leaving South Korea, Clinton said the United States and other nations hoped that the flickers "will be ignited into a movement for change that will benefit the people of the country".

The secretary of state told reporters that she would look to "determine for myself what is the intention of the current government with respect to continuing reforms, both political and economic".

Clinton has said she will insist that Myanmar free all political prisoners -- activists' estimates vary between 500 and more than 1,600 -- and move to end long-running ethnic conflicts that have displaced thousands of people.

Senior administration officials said Clinton would not announce an end to sweeping economic sanctions on Myanmar, a step that would require approval by Congress. But top US diplomats rarely undertake such high-profile visits without being ready to offer some incentives for further action.

On Thursday Clinton will meet President Thein Sein, a former general now at the vanguard of reforms, before flying later in the day to Myanmar's dilapidated main city Yangon to confer with democracy leader Aung San Suu Kyi, whose views hold great sway in Washington.

US policymakers acknowledge that they know little about Myanmar's inner workings and many believe the government remains deeply suspicious of the outside world.

The military is thought to have been so convinced of the possibility of a US invasion that it abruptly shifted its capital inland in 2005, and refused American assistance three years later when Cyclone Nargis left an estimated 138,000 people dead or missing.

China has been the primary supporter of the junta and the military-dominated civilian government that succeeded it after controversial elections last year, but many ordinary citizens are resentful of Beijing's economic influence.

Ahead of Clinton's trip, Myanmar's military chief visited Beijing to reaffirm friendly relations, although Thein Sein stunned observers recently when he bowed to public opposition and stopped a dam that would benefit China.

A Chinese state-run newspaper warned Wednesday that Beijing would defend its interests in the resource-rich neighbour.

"China has no resistance toward Myanmar seeking improved relationships with the West, but it will not accept this while seeing its interests stamped on," the Global Times daily said of Clinton's visit.

Suzanne DiMaggio, who led a task force on Myanmar policy for the New York-based Asia Society, said Clinton's trip marked the latest US effort to curb the influence of a rising China.

"The Obama administration recognises that this moment of change is an opportunity for the United States to help move Burma away from authoritarian rule and into the world community," she said.

Myanmar once supplied food across Asia and until World War II the country enjoyed some of the continent's highest standards in literacy and health.

But the country now languishes near the bottom of global rankings of human development.

While it exports gas and other lucrative products to neighbouring nations, ordinary citizens have seen little benefit, and the nation remains under tight US and European sanctions.

The only other US secretary of state to visit Myanmar was John Foster Dulles in 1955.