Organisers of the anti-Abbott grassroots movement say demonstrator numbers have halved as public despair over the lack of protest progress begins to sink in.

Despite an estimated 40,000 protesters marching against the coalition government over the weekend, it was less than half the number of people who turned up in March.

March Australia co-ordinator Jane Salmon said organisers were thrilled with the spirit of the protests, but the campaign had begun to lose steam.

"Some despair is sinking in, and the marches are not changing things," Ms Salmon said.

Ms Salmon also said competing rallies and wet weather had dampened turnout.

As many as 10,000 grassroot campaigners rallied in Sydney's Hyde Park demanding changes to the government's climate change, education, environmental health, indigenous rights and immigration policies.

One of the six speakers, NSW Nurses and Midwives Association president Coral Levett told rally goers it was up to them to fight changes to the proposed Medicare levy along with other budget cuts.

"We have to keep fighting to stop these unjust, regressive budget measures," Ms Levett said.

"We must call on our MPs, particularly those in the Senate to reject these abhorrent attacks on Medicare in the form of co-payments."

The protest shut down the CBD for around 30 minutes as protesters peacefully marched to Sydney Town Hall before returning to Hyde Park for a free concert by popular indie band The Jezebels.

Meanwhile in Melbourne, human rights advocate and lawyer Julian Burnside told around 10,000 protesters they can expect to see Tony Abbott in the dock in an international court.

"The way they are treating refugees in Australia is a crime, and there has already been a reference put into the international criminal court complaining of that very treatment," Mr Burnside said.

"If you feel exhausted keeping up the pressure on the government, if you feel so tired you can't keep going, just support yourselves with the vision of Tony Abbott and Scott Morrison in the dock at The Hague."

The crowd also jeered as a large Tony Abbott puppet waved at them with smoke coming from its rear, representing a person with their pants on fire.

In Brisbane, organisers blamed complacency for a relatively poor turnout.

The Queensland government's anti-bikie laws and plans to sell assets were among the issues discussed, as well as the plight of refugees and the Great Barrier Reef.

Organisers claim 5000 people took part in Sunday's rally but police say no more than 1200 participated in the Brisbane CBD protest.

There were no arrests across the three capital cities.