'Dangerous' threat to emerge from anti-migrant rallies

March for Australia, the group behind the rallies, said the gatherings would demand the federal government end "mass migration".

Michael Zekulin, a terrorism researcher at the Australian National University, said violence could erupt if people started identifying with one group at the expense of others in the community.

"This is where things can become potentially dangerous when you have individuals who are sort of espousing or blaming other groups for the problems of their group," he told AAP.

"If that starts to get out of hand, if there are confrontations, that can sort of feed into larger things as they pick up more momentum."

Anti-racism marches will also be taking place at the same time in Sydney and Melbourne that could see the rival groups come head-to-head.

NSW Police will be sending up to 1000 officers to patrol parts of the inner-city, while Victoria Police will declare the Melbourne CBD a designated area, allowing people to be searched for weapons and be asked to remove face coverings.

Dr Zekulin said social media had played a role in encouraging copy-cat behaviour among extremist groups.

"It's very clear that these individuals travel in the same circles on the internet," he said.

"They see each other, they see what other groups who have similar beliefs to them are doing, and then they will try to imitate or mimic that."

Indian migrant workers have expressed fears they will be targeted by protesters at the anti-migration rallies.

The Albanese government has declared there is no place for hate in Australia.

While the coalition has called for unity and respect for diverse communities, hitting out at reports particular non-white ethnic groups might be targeted.

Greens Immigration spokesperson David Shoebridge said anti-migrant rhetoric inside parliament house and in the media had fed into extremist views.

"We are in solidarity with every community that is targeted and concerned by these hateful rallies," he said.