France and Australia are fighting a war to protect the shared values forged in the muddy trenches of the Great War, the French ambassador said in the wake of the Paris attacks.

Speaking outside a packed service at St Andrew's Cathedral in central Sydney to commemorate the 129 lives lost on Friday, Christophe Lecourtier said the battle being waged was not against Islam.

"When we talk about war ... it's not a war against the Muslims or Islam or any religion," he told reporters.

"It's a war to protect our values and [there] are not that many countries in this century that do share the same values.

"Australia is one of these countries that share the same values as France because we forged them together in the muddy trenches of northern France."

Islamic State (IS) has claimed responsibility for the attacks, carried out across six locations in the French capital.

"We know what we fight," Mr Lecourtier said. "After a period of mourning, France shall never surrender."

Mr Lecourtier was joined at the St Andrew's service on Sunday afternoon by France's consul-general in Australia, Nicolas Croizer, NSW Premier Mike Baird, Governor David Hurley, and Deputy Police Commissioner Nick Kaldas.

Police manned each of the cathedral doors as the service opened with the Australian anthem. It closed with the national anthem of France.

Anglican Archbishop of Sydney Glenn Davies told the congregation – including many French people living, working or studying locally – that the service of sorrow and prayer was designed to give people hope.

Another service will be held at St Mary's Cathedral on Monday evening, while a vigil is planned for Melbourne's Federation Square on Monday night and a similar event is expected to be held in Adelaide on Tuesday evening.

The French flag was raised over the Harbour Bridge on Sunday morning as town hall flags around the city were flown at half-mast to mark the attacks.

The Opera House will continue to display the blue, white and red for the next two nights.
A condolence book will be opened at the French embassy in Canberra tomorrow and a minute of silence will be observed there at 10:30am.

The Muslim community in Australia is already fearful of reprisals. One woman told Fairfax Media Muslims, particularly women, feared going out in public without a male friend to accompany them.

Organisers of anti-Islam "Reclaim Australia" rallies planned across the country for Sunday, November 22, were also taking to social media to use the Paris attacks to bolster support for their cause.

And anti-racism groups were pushing back, promoting their counter-rallies to take place at the same time.