Protesters have jumped on Lord Mayor Robert Doyle's car outside the National Gallery of Victoria this evening.

PROTESTERS have jumped on Lord Mayor Robert Doyle's mayoral car outside the National Gallery of Victoria.

Up to 100 protesters ambushed Cr Doyle's car as he approached the NGV about 6.50pm to attend the Institute of Public Affairs' 70th anniversary dinner.

Cr Doyle told the Herald Sun that the protesters had surrounded his car, hammering on the windows, jumping on the bonnet and sitting on the roof, ''hammering their heels'' against the windscreen.

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Speaking five minutes after the incident, Cr Doyle said he and his driver were unhurt.

''What a disgrace,'' Cr Doyle said of the protest.

''This wasn’t just a protest, this was violent, hate-filled.

''I have never experienced anything like this in 25 years of public life.''

Federal Opposition Leader Tony Abbott, News Corporation chairman Rupert Murdoch, mining magnate Gina Rinehart and Archbishop George Pell were invited guests.

Police were forced to drag the protesters off the car to free Cr Doyle - who was trapped inside for at least five minutes.

A force response unit helped cleared the path and the car drove off.

Cr Doyle said the protesters had spotted his car as he pulled up to park outside the NGV and surrounded it, shouting and waving placards.

''What a disgrace that people who are supposedly protesting about freedom of speech, rights and respect behave in that manner,'' he said.

''There was no way I was going to get out of the car into that mob.

''The police were terrific - I have the highest praise for them. They recognised what was going on and pulled people off the car and cleared a path for me.''

Cr Doyle said the male and female protesters were carrying signs that said things such as ''eat the rich'', and they had broken the signs into pieces and smashed the wood into his car.

''This is not protest, this is assault,'' he said.

Cr Doyle said he returned to the gallery after the incident to hear Rupert Murdoch's speech at the dinner, determined not to let "self-righteous d---heads" ruin his night.

''They let our tyres down,'' he said.

''We had to go and get them re-inflated but we’ve done that and I’m not going to let them (the protesters) stop me attending.''

A protester, who would not give his name, said it was ''just bad timing'' for Cr Doyle to arrive as protesters were leaving the scene.

Witness Don McDonald said: "They were just bashing the bonnet. There would have been about 50 or so people surrounding the car.

''They were chanting, 'whose streets our streets' and that sort of thing.

''Then the police came and moved them off the road.''

Victoria Police Sgt Peter Mellas said the incident may be investigated at a later date.

''We were not expecting this from the protesters. Everyone is entitled to protest as long as they do it in the confines of the law,'' Sgt Mellas said.

''...There may be a matter of investigation, we will have to wait and see.''

Police spokeswoman Belle Nolan said there had been no arrests, assaults or injuries.