Australia's Aboriginal "tent embassy" has come under the spotlight again after a second day of trouble at the 40-year-old protest site in Canberra.

Embassy protesters burned and spat on the Australian flag on the front steps of Parliament House the day after they chased Prime Minister Julia Gillard and opposition leader Tony Abbott from a restaurant near the camp.

In the latest incident, a crowd of up to 400 protesters marched from the embassy outside Old Parliament House to the front verandah of the new parliament building to face a heavy police presence. The crowd was prevented from entering Parliament House by a 60-strong human wall of armed police.

Police are investigating whether setting fire to the flag broke the law.

Ugly scenes erupted on Australia Day as members demonstrated in a protest over their long-running fight for equality and land rights.

The embassy emerged 40 years ago when four Aboriginal men - Michael Anderson, Billy Craigie, Tony Coorey and Bertie Williams - arrived in Canberra from Sydney and planted a beach umbrella on the lawn in front of Parliament House, now called Old Parliament House.

The umbrella developed into the camp in response to the McMahon coalition government's refusal to recognise Aboriginal land rights. Aboriginal people and non-indigenous supporters joined the protest from all over the country.

During the first six months of its life the embassy succeeded in uniting Aboriginal people throughout Australia in demanding uniform national land rights and organising widespread non-indigenous support for their battle.

The embassy has been branded an "icon" and an "eyesore".

The protesters' Facebook page, which has more than 2,000 members, lists them as a political organisation although the group is not formerly recognised as an official embassy by the government.

On January 26, a public holiday, the embassy invited supporters and other members of the public to the site to celebrate "Sovereignty Day".

The intention, according to the embassy's website, was to mark 40 years since the first protest on site.

But tensions erupted and embassy members banged on the windows of a nearby restaurant where Gillard and Abbott were present for an Australia Day function.

Dramatic video images of Gillard were splashed across the media. In the melee as she scrambled from the restaurant she tripped and lost a shoe while being dragged to safety by her bodyguards and being driven off in a car pursued by angry demonstrators.

Aboriginal elder Ben Taylor Cuiermara told ABC news that despite seeing little change in the last 40 years the fight had not been in vain.

"I want to see justice. I want to see us get land rights. Somewhere to take my people out of this bondage," he said.