In recent months, there have been a number of protests at the Elbit Systems building.
Protesters have reportedly blocked Greenacres Road with a caravan and chained themselves to a vehicle, as well as gates at the former Ferranti Technologies building.
Campaigners have been there since around 6.30am this morning (Monday).
The site, at Cairo House on Greenacres Road, has been targeted again in the latest of a number of 'successful actions' taken by Palestine Action against Elbit Systems, their subsidiaries, landlords, and partners.
Arms company Elbit bought the formerly British-owned Ferranti Technologies site for £15 million in 2007.
A Palestine Action spokesperson said this morning: "The activists currently occupying the Elbit Ferranti factory have once again shown the power of direct action against Israeli oppression.
"While Western governments continue to side with the oppressors, and while media attention in Palestinian suffering has dwindled, Palestinians are still exposed to daily brutality, starvation, apartheid and death.
"These activists are bravely standing against this injustice - and we will continue to do so until Elbit is shut down."
