Pictures show people on the shore looking across at the main building on the pier with its roof almost entirely consumed by flames.
Pier fire ‘dry run’ just months ago
A small fire in wall panelling is believed to have started the bigger blaze.
East Sussex Fire and Rescue Service said: “Around 60 firefighters are now in attendance and tackling the fire. They were called out at 3.13pm.”
A spokesperson told Channel 4 News the 12 fire engines are manned by crews who did a full fire simulation on the pier eight months ago on 3 December 2013.
There are no reported casualties but it is believed tourists were walking on the pier when the fire began.
Sussex Police said they had officers at the scene to help with local road closures and to prevent the public getting too close to the fire.
Photographs shared on Twitter show beachgoers and sunbathers calmly watching the blaze, dressed only in swimming gear.
Eastbourne pier was opened in 1870 but finally completed in 1872.
Fate of the pier - a history of seaside fires 2010 - Grade-II listed Hastings Pier almost destroyed by fire 2008 - Grand Pier in Weston-super-Mare badly damaged by fire 2008 - Fleetwood pier in Lancashire destroyed by fire and demolished 2005 - Southend-on-Sea Pier in Essex, the longest pleasure pier in the world, badly damaged by fire 2003 - West Pier in Brighton wrecked by two major fires within two months