Hundreds of people have gathered outside Sydney's Town Hall to protest against any moves to water down Medicare and introduce patient payments to see a bulk-billing GP.

Waving banners reading "Stop Abbott, Save Medicare, Free Universal Health Care, the rally has called for the government to rule out any changes to Medicare.

Speaking at the demonstration, deputy opposition leader Tanya Plibersek paid tribute to the introduction of the health system, which is celebrating its 30th anniversary this month.

"Before Medicare millions of Australians used to be bankrupted.

"Medical bills were the highest cause of bankruptcy in Australia, as they still are today in the United States," she told those gathered.

She called for the government to rule out any introduction of a GP co-payment, which would require patients to fork out a suggested $6 per consultation.

It comes just weeks after Prime Minister Tony Abbott dismissed claims that the government was planning to introduce a fee, as nothing more than a scare campaign.

"Nothing is being considered, nothing has been proposed, nothing is planned," Mr Abbott told reporters earlier this month.

But Ms Plibersek told reporters on Saturday that on "the very same night on the 7.30 Report, (Treasurer) Joe Hockey said nothing is off the table".

She said while the fee is small, if it was introduced it would be prohibitive for some and would ultimately cost the system more.

"What we know is that any illness treated early is much better for the patient and much better for the health system," she said.

General Secretary of the NSW Nurses and Midwives Association (NSWNMA) Brett Holmes said he didn't want a system where the question of money is the first thing that is asked when a patient walks in the door.

"If that forces too many people into the hospitals, we will put a co-payment on emergency department services as well.

"This is an idea that will be expanded and expanded if it happens."