Tensions could flare between anti-war protesters and police as activists signal significant actions on the final day of a controversial weapons expo.

Rally organisers are expecting “significant protest activity” on Friday as the Land Forces weapons expo winds down in Melbourne following days of unrest.

“There will be renewed vigour to protest because it’s the last day,” organiser Caroline Da Silva said.

“It’s our last chance to show these weapons companies that they’re not welcome here.”

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 bottle “missiles” were launched 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 re-grouped 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.

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 duration of 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.

“We’re here because we are people of goodwill and good spirit who want to see peace, justice and freedom – so there’s nothing that police violence can do to change that.”