Police and protesters have already clashed after thousands of people descended on Melbourne’s CBD to rally outside a major defence and weapons expo.

Hundreds of police were also outside the Melbourne Convention and Exhibition Centre early on Wednesday, where more than 25,000 activists were expected to disrupt the Land Forces exposition.

There were early clashes between protesters, who were chanting pro-Palestine slogans through a loud speaker, and police. Former Merri-Bek councillor James Conlan posted a video to Facebook of hundreds of protesters.

He described the expo as “the peak gathering of global war mongers who commit genocide and war crimes with the showcased weapons”.

“The more people here, the better,” he said.

Among those expected to be there is Greens MP Gabrielle Di Vietri, who said she would skip parliament to go.

“The Labor government sponsoring a deadly weapons expo, that might be worth skiving off an hour or two of parliament,” Di Vietri said on Tuesday.

“There has rightfully been a huge other outcry, tens of thousands of protesters are expected to resist this expo going ahead, they don’t want to see more profiteering on our doorstep.”

But Victorian Treasurer Tim Pallas warned anyone who did not need to be in the area should stay away.

“If you have no business being there, if you’re not there protesting, I wouldn’t encourage anybody to be there,” he said on Tuesday.

Yarra Trams has warned commuters of disruptions to city-bound services, including routes 96 and 109.

Pallas said police had asked the state government for additional funds to cover the event, estimated to cost up to $15 million.

Victoria Police expected it would be its biggest operation since chaos at the World Economic Forum in 2000.

Hundreds of regional officers have been brought to Melbourne for the event, along with general duties officers and specialist police. They include the public order response team, highway patrol and mounted branch.

There is also a checkpoint across the road from the convention centre where delegates credentials are checked before entry.

A police spokesperson said there had been a big effort to ensure the “highest level of safety and security”.

Disrupt Land Forces spokeswoman Jasmine Duff said the protest was triggered by the federal government’s stance on the conflict in the Middle East.

“We’re protesting to stand up for all those who have been killed by the type of weapons on display at the convention,” she said.

“Many of the weapons inside the convention centre are advertised as battle-tested. In the context of Israeli weapons firms, which are present, this means tested through killing civilians in Gaza.”

Protesters were expected to march through Melbourne’s CBD later on Wednesday.

The Land Forces International Land Defence Exposition is not open to the public. It runs until Friday.

-with AAP