The circle aimed at highlighting climate change measure 300ft across and features the Extinction symbol and follows a similar one at Glastonbury earlier this summer.
The Extinction Rebellion group said it was using the symbol to draw attention to climate chaos.
Four days of music started at Charlton Park on Thursday.
Organisers said: "#WOMAD2019 has been absolutely amazing so far. Saturday and Sunday day tickets on sale now, so don't miss out on everything else in store at #TheWorldsFestival > www.womad.co.uk/tickets"