Gaza war protesters and police have clashed outside an arms fair in Australia.

About 1,200 people attended the protest on Wednesday, picketing the Land Forces 2024 exposition being held in Australia’s second largest city of Melbourne, authorities said. Police used sponge grenades, flash-bang devices and irritant sprays against a rowdy crowd, and arrested dozens.

Pro-Palestine slogans were chanted through loudspeakers and Palestine flags waved. Police were pelted with rocks, horse manure and bottles filled with liquid as they tried to protect attendees of the expo, some of whom were assaulted by protesters, a Victoria state police spokesperson said in a statement.

The protest was organised by the Students for Palestine and Disrupt Wars groups. Police arrested 33 people for offences including assault, arson and blocking roadways.

Australian media reported it was the largest police operation in Melbourne since 2000, when the city hosted the World Economic Forum.

About 1,000 exhibiting organisations from 31 countries are expected to attend the event, which runs until Friday. Organisers branded it Australia’s largest defence expo.

Prime Minister Anthony Albanese said people had the right to protest but had to do it peacefully.

“You don’t say you’re opposed to defence equipment by throwing things at police. They’ve got a job to do and our police officers should be respected at all times,” Albanese told Channel Seven.