A sniper poised and ready to fire while perched on the roof of a shrine was part of the security measures at dawn service commemorations in Melbourne.

The sniper was present at the Shrine of Remembrance in the Victorian capital for Anzac Day services early on Thursday morning.

About 25,000 people gathered there to remember those who fought and died for Australia in various wars.

Victoria Police said there was no increased safety threat for the day, before an alleged ISIS terrorist was arrested over a plot to attack people marking Anzac Day in Gallipoli.

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A sniper poised and ready to fire while perched on the roof of a shrine was part of the security measures at dawn service commemorations in Melbourne

Addressing the pre-dawn crowd, Victorian Premier Daniel Andrews urged them to care for 'the next generation of Anzac'.

'How can we possibly thank so many for giving so much?' he asked.

'Stand here at this hour in this still dark, sacred place and remember them, remember that they came from every corner of Victoria and Australia, every walk of life, every background.'

On Wednesday, Victoria Police acting superintendent Craig Peel said there would be a 'zero-tolerance approach to anti-social behaviour'.

About 25,000 people gathered at the Shrine of Remembrance to remember those who fought and died for Australia in various wars

He said he wasn't concerned that attacks in Sri Lanka which killed more than 300 people would have an impact on security at the dawn service.

'There is no intelligence at all to suggest that any of these events that we're running across the state are a target for any sort of behaviour that would be detrimental to them being run safely,' he said.

NSW Police also reassured people there was no increased threat to the safety of those attending dawn services on Anzac Day.