Chaos is unfolding at the Melbourne Cup with a man arrested on the train tracks and protesters scaling a crane to hang a banner over the racetrack.

Police detained the man close to a parked car blocking trains to Flemington, according to 7 News.

Meanwhile, two female demonstrators climbed a crane to hang an "Evacuate Manus" banner over the crowd watching the race that stops a nation.

The group Whistleblowers, Activists & Citizens Alliance have taken responsibility for crane protest, sharing photos of the stunt on social media.

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"2 women have climbed a crane at #melbournecup with a banner that reads 'SOS. Evacuate #Manus now' #justice4refugees," wrote WACA on Twitter.

Victoria Police told news.com.au the situation was unfolding and they will make a statement shortly.