Officers blocked Senator Thorpe from approaching anti-transgender activist Kellie-Jay Keen-Minshull on the lawns before Parliament House.

Senator Thorpe approached the rally's speaker tent, shouting "you are not welcome" before she was stopped by a private bodyguard and Australian Federal Police, falling to the ground in the altercation.

Australian Federal Police have confirmed an incident between protesters and police will be reviewed by police's internal integrity team. It's not yet confirmed to be related to Senator Thorpe.

The British anti-trans activist, also known as Posie Parker, arrived in Canberra on Thursday to speak as part of a tour of Australia.

Ms Keen-Minshull claims to advocate for women's safety but has been criticised for spreading misinformation and hatred against transgender people.

Wrapped in an Aboriginal flag, Senator Thorpe crawled from police who had blocked her from approaching Ms Keen-Minshull.

She then walked 20 metres away to join a counter-rally opposite, organised by Australian National University students.

In comments made shortly after the incident, Senator Thorpe alleged she had been "pulverised" by the federal police.

"I went to tell her [Ms Keen-Minshull], that thing, that they are not welcome here," she said.

"And I got pulverised by the police for simply telling that person that they are not allowed to be here."

Greens justice spokesperson senator David Shoebridge said the Greens, of which Senator Thorpe was a member until earlier this year, have sought an "urgent briefing" with the AFP following the incident.

"Across the country we have seen these acts of nonviolent protest and solidarity for the trans and gender-diverse community, which are repeatedly drowning out the transphobes," he said.

"The Greens have sought an urgent briefing from the AFP and the government about the use of force towards Senator Thorpe that saw her thrown to the ground.

"We need to ensure police are deescalating violence at rallies and never add to the potential for physical confrontation."

READ MORE:

Just before 1pm, the anti-trans protest comprised approximately 30 people, while 140 people gathered to counter-protest. Approximately 20 police officers were also on the scene.

An incident between federal police and protesters at the rally has been referred to the federal police's professional standards command.

"The interactions between the AFP and protesters will be reviewed, and an incident has been referred to the AFP's professional standards sommand," an AFP media statement said.

"Given a matter is now under investigation, no further comments will be made."

Protesters and counter-protesters began to leave the event, which began at 12pm, at about 2pm, when Ms Keen-Minshull was invited into Parliament House by One Nation senator Malcolm Roberts.

Senator Roberts attended alongside One Nation senator Pauline Hanson and independent senator Ralph Babet to support Kellie-Jay Keen's appearance.

Greens senator Janet Rice joined counter-protesters as they chanted "f--- you, Posie, f--- you" over Ms Keen-Minshull's speech.

ACT MLAs Jonathan Davis, Emma Davidson, Rebecca Vassarotti and Andrew Braddock also stood with the counter-rally protesters, carrying transgender pride flags.

People attending the counter rally, who outnumbered the anti-trans protesters, chanted over Ms Keen-Minshull's speech.

Wren Somerville, one of the counter-rally's organisers and a member of LGBTQI advocacy group Equal Love, said it was important to push back against hateful views.

"I think building up [counter-protests] like this is the best way to push that politics back, to relegate it. That's how we did it with homophobia," he said.

"I think demoralising right-wing transphobes is a really good step in the right direction."

Ahead of the rally, ACT Chief Minister Andrew Barr said "campaigners who promote social exclusion and inequality will find little support in Canberra".

"The ACT government supports the realisation of LGBTIQ+ equality as part of our broader commitment to social inclusion and equality," the chief minister said in a statement.

"The right to equality is enshrined in the ACT's own Human Rights Act 2004, which we are proud to have been the first jurisdiction in Australia to enact."

On Saturday, an event organised by Ms Keen-Minshull's Let Women Speak group was attended by approximately 30 men, dressed in black, who performed Nazi salutes on the steps of the Victorian Parliament.

They also carried signs with offensive names for transgender people written on them.