A woman has been arrested after she was found "bolted" to the steering wheel of a car parked on the train line to Flemington Racecourse as part of a protest, police say.

Key points: A group calling itself the Whistleblowers, Activists & Citizens Alliance claims responsibility for the protest

A group calling itself the Whistleblowers, Activists & Citizens Alliance claims responsibility for the protest The car's tyres had been let down and it was covered in protest messages

The car's tyres had been let down and it was covered in protest messages About 20 protesters were at the scene when police arrived

Police beefed up their presence at the Melbourne Cup as a result of the protest, and another in which two women scaled a crane to unfurl a banner, which read "SOS: Evacuate Manus Now".

A group calling itself the Whistleblowers, Activists & Citizens Alliance (WACA) claimed responsibility.

The car's tyres had been let down and it was covered in similar protest messages.

It caused major delays on the Flemington Racecourse train line, and racegoers were forced to get off a train and walk along the tracks to the racecourse.

Victoria Police Superintendent Tim Hansen said about 20 protesters were at the scene when police arrived.

"They left the vehicle in situ with the tyres let down, and a female protester was bolted to the steering wheel of that vehicle," he said.

"Police attended, all other protesters decamped immediately, and with the assistance of MFB we extracted that female from the vehicle and she was arrested."

The car blocked a train bound for the Melbourne Cup. ( ABC News )

Racegoers were forced to get off the train and walk. ( ABC News )

The woman, a 27-year-old from Moonee Ponds, was still being interviewed by police and was likely to be charged with offences including reckless conduct endangering life, Superintendent Hansen said.

Two other protesters, Hannah Patchett and Katherine Woskett, abseiled from a crane at Flemington about 12.30pm to unfurl the protest banner.

"We are joining with others across Australia to demand that the Government evacuate the men on Manus immediately and bring them to safety for processing," WACA spokeswoman Charlotte Lynch said.

Superintendent Hansen said those women were interviewed, but no charges had been laid yet.

"Police immediately made contact with the protest group and successfully negotiated an outcome where those protesters removed themselves from the crane after a period of time," Superintendent Hansen said.

He said police were generally happy with crowd behaviour, but seven people were evicted for drunkenness and "general offending", and another two were arrested for drunkenness.

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The WACA group has a history of civil disobedience. Last year, protesters scaled Parliament House in Canberra and glued their hands to the public gallery.

Australia's detention facility on Manus Island, which housed 600 men, was permanently closed at the end of October and returned to the Papua New Guinea Defence Force.

The PNG Government told the men they had to move to new accommodation in the town of Lorengau, after the country's supreme court ruled the detention facility was unconstitutional.

Power, water and the food service has now been cut off to the site.

However, the men have been reluctant to leave, fearing for their safety, and had been stockpiling water in the lead-up to the closure of the centre.