The country has been in turmoil since last year's coup, with mass protests and a subsequent military crackdown that has killed more than 1,500 civilians, according to the UN's human rights office.

Junta chief Min Aung Hlaing issued the "pardon order" -- a regular feature of major holidays in the country -- for 814 prisoners, state media said, marking the 75th Union Day.

The annual holiday commemorates an agreement between independence hero Aung San and several ethnic groups to form a Union of Burma independent of British rule.

Those given amnesty will be mostly from prisons in commercial hub Yangon, junta spokesperson Zaw Min Tun told AFP.

He did not say whether Australian academic Sean Turnell -- who has been detained for more than a year -- would be among those released.

The economics professor was working as an adviser to civilian leader Aung San Suu Kyi when he was arrested last February, days after she was ousted by the military.

He has been charged with violating Myanmar's official secrets law and faces a maximum penalty of 14 years in prison if found guilty.

About 100 people gathered outside Yangon's Insein prison on Saturday morning hoping to be reunited with loved ones, AFP correspondents said.

Four minibuses left the prison around noon local time (0530 GMT) and drove away, with those inside waving as people in the crowd shouted the names of relatives.

Thin Thin Aye, 46, waited in the hope her son -- jailed last year for incitement against the military -- would be among those freed.

She kept waiting even after the last bus pulled away and prison staff said no other prisoners would be released.

"I hope my son will be released as soon as possible and I want him to stay with our family," she told AFP through tears.

- 'Where was the union?' -

The junta marked Union Day with a show of force in the military-built capital Naypyidaw.

Hundreds of troops paraded alongside civil servants waving national flags in unison, and there were choreographed dances.

Helicopters carrying the country's yellow, green and red flag flew overhead, followed by jets trailing the same colours in smoke.

In a speech to troops, Min Aung Hlaing repeated the military's claim of massive fraud in 2020 elections won by Suu Kyi's party.

He also invited the myriad ethnic armed organisations that have been fighting Myanmar's military -- and each other -- for decades to sit for peace talks.

The Karen National Union, whose fighters have clashed repeatedly with junta troops in the east, said it would not attend talks.

"They say it was union day, but where was the union?" spokesman Padoh Saw Taw Nee told AFP. "They stole power from the civilian government. They are not the official government."

"The message for Union Day is at complete odds with the reality that is Myanmar," said independent analyst David Mathieson, adding the junta was not sincere about peace.

"It's pretty absurd that on the 75th anniversary of Union Day the country is more divided than at any point in its history."