Rally organisers are expecting "significant protest activity" on Friday, as the Land Forces weapons expo winds down in Melbourne following days of unrest.
Before 9am, one female protester affixed herself to the back of a hatchback after it appeared she chained herself to the inside the vehicle, ABC reported.
The car was moved off the road near the Kings Way intersection south of Flinders Street at Southbank before the woman was detached from the vehicle by police.
The Spencer Street bridge remains blockaded with dozens of police present.
Protest organiser Caroline Da Silva said "there will be renewed vigour to protest because it's the last day".
"It's our last chance to show these weapons companies that they're not welcome here," she said.
The first day of the expo on Wednesday descended into violence and chaos after wheelie bins were set alight and horse manure, food-grade acid and glass bottles were hurled at police barricades.
Riot officers returned fire on the 1500 demonstrators with rubber bullets, tear gas and flash-bang devices, leading to 42 people being arrested.
But scenes were more subdued on Thursday, as a few hundred protesters marched towards the convention centre before dispersing.
They later regrouped outside the Bourke Street offices of defence contractors Hanwha Defence and Elbit Systems to oppose deals between the companies and governments, blocking access to cars and trams.
Protest scenes were more subdued outside the Melbourne offices of two defence contract companies. (Con Chronis/AAP PHOTOS)
Protesters say weapons on display inside the expo have been used on civilians in the Gaza conflict.
Police and political leaders condemned the "disgraceful" actions and tactics used by activists, labelling them "thugs".
Police Commissioner Shane Patton lashed out at "hypocritical" protesters, warning the largest deployment of officers in two decades would be prepared for any event for the conference.
Mr Patton's denunciations have not deterred activists, with Ms Da Silva vowing the demonstrators were "here for the long haul".
"A bit of police spray, some rubber bullets - those things are harmful - but they don't do anything to alter our conscience," she said.
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