Protesters are targeting an arms fair hailed as "the world's largest gathering of the defence and security community".
About 60 people gathered in Royal Albert Way, which leads to the ExCeL London centre where the four-day Defence and Security Equipment International (DSEI) event starts on Tuesday, September 14.
Activist Sarah Wilkinson said: "We may not stop it, but we've got to make clear it is not welcome in this country."
Campaigners allege the arms on sale could be used by oppressive regimes to commit human rights abuses and war crimes.
A DSEI spokesperson said the fair is "world-leading" and showcases the important role the UK's defence and security sector plays on the global stage.
He added DSEI provides an effective platform for an industry which has a turnover of £486billion and employs more than 290,000 people.
"DSEI serves only the legitimate defence and security industry, which is the most highly and tightly regulated in the world," he said.
Groups including Newham Against the Arms Fair, Palestine Solidarity Campaign and Black Lives Matter are campaigning against the event.
Protesters sat in the road in a bid to stop military vehicles and equipment getting into the centre.
Scotland Yard denied claims from activists that it is using facial recognition technology to target protesters.
The mayor of Newham, Rokhsana Fiaz, said: "It is abhorrent such an event should happen in Newham.
"Newham Council resolved to oppose DSEI in 2019 and our message to the arms traders remains that you are unwelcome - don’t come back in the future."
Mayor of London Sadiq Khan has signalled his opposition to DSEI at ExCeL London, partly due to the cost of policing protests. In 2019, this amounted to £2,407,574.
A spokesperson said ExCeL London respects the right to conduct lawful protest, but at the same time is doing everything it can to ensure minimum disruption to people who live and work in the area.
Amber, an activist who only gave her first name, denied protesters were causing disruption and urged residents to join in.
To date, a man and woman have been arrested on suspicion of vehicle interference. This compares to 116 arrests made in 2019.
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