On the busy assembly line at Gazelle, one of the top Dutch bike manufacturers, a quiet revolution is taking place: Mixed with wheels, brakes and saddles are now batteries and engines.

Sales of electric bikes are soaring across Europe, particularly in the Netherlands and Germany, and three out of every 10 cycles made by Royal Dutch Gazelle are equipped with some motorised help.

It's giving a welcome boost to the European bicycle industry as it squares up to stiff competition from Asian companies.