A surge in the number of people buying adult colouring books has threatened pencil stocks world-wide as manufacturers struggle to cope with an increased demand for quality crayons.

The world’s biggest wooden pencil manufacturer, Faber-Castell, say they are experiencing "double-digit growth" in the sale of artists’ pencils and have been forced to run more shifts in their German factory to keep up.

“The production of our artists’ pencils has increased strongly compared to the previous year,” Sandra Suppa from Faber-Castell told the Independent.

“Currently, we are running more shifts than usual in our factory in Stein, Bavaria in order to satisfy the global needs for artists pencils related to the colouring trend for adults.

Pencil manufacturers Staedtler and Stabilo are also struggling to keep up with demand Faber-Castell (Faber-Castell)

“The trend is continuing to this day and can be felt globally – from South America to Asia.”

Brazil has reported pencil shortages after many Brazilians jumped onto the colouring book bandwagon, The New York Post reports.

While, the famous European pencil manufacturers Staedtler and Stabilo are also struggling to keep up with demand, according to the New Zealand Herald.

The 12 best colouring books for adults Show all 12 1 /12 The 12 best colouring books for adults The 12 best colouring books for adults Enchanted Forest: An Inky Adventure & Colouring Book: £5, amazon The 12 best colouring books for adults Calming Colouring Nature Patterns by Graham Leslie McCallum: £7 amazon The 12 best colouring books for adults The Mindfulness Colouring Book by Emma Farrarons: £4, amazon The 12 best colouring books for adults The Time Garden by Daria Song: £5, amazon The 12 best colouring books for adults Tropical Wonderland: A Colouring Book Adventure: £4, amazon The 12 best colouring books for adults Animorphia by Kerby Rosanes: £7, amazon The 12 best colouring books for adults Dream Cities by Rosie Goodwin and Alice Chadwick: £5, amazon The 12 best colouring books for adults Fill Me In by Moose Allain: £10, amazon The 12 best colouring books for adults The Creative Colouring Book for Grown Ups by Various: £8, amazon The 12 best colouring books for adults Field Guide: Creatures Great and Small by Lucy Engelman: £11, amazon The 12 best colouring books for adults Cats: 70 Designs To Help You De-Stress: £8, amazon The 12 best colouring books for adults Colour Me Good Eddie Redmayne by Mel Elliot: £8, amazon

Ms Suppa said the colouring book craze’s ripple effect on the pencil industry could be felt in an increased want for higher quality pencils and a better variety of colours.

“People are now not satisfied with ‘just’ 36 colours and we are noticing a trend in people preferring bigger sets of 72 or even 120 colours for colouring.

“We are also noticing that people are investing in our highest quality artists’ pencils.”

The colouring trend can be 'felt globally' Faber-Castell (Faber-Castell)

Colouring books have become a surprising feature of many bookshops’ bestsellers lists in recent years, with Waterstones previously noticing a 300 per cent rise in sales in just one year, the Telegraph reports.

Melissa Cox, head of children’s buying at Waterstones, told the paper: “Colouring books are doing really well at the moment, which initially surprised us… and we realised adults were buying them for themselves.”

She added there had been a prominent increase in demand for challenging and intricate designs to fill in.

This Van Gogh documentary will be the first ever fully-painted feature film

Bestselling titles include Millie Marotta’s Animal Kingdom, Emma Farrarons' The Mindfulness Colouring Book and Johanna Basford’s Secret Garden.

Ms Basford, whose colouring books for grown-ups have sold some 16 million copies worldwide, including three million in China alone, told the Sunday Telegraph: "People like colouring-in because they are fed up with digital.

“There is something nice about picking up a pencil and a pen. You are not going to get interrupted by Twitter, and there is also a childhood nostalgia element to it.”

Faber-Castell attributes the sudden rise in adult colouring-in to the hobby's “relaxing and meditative nature”.

“It allows you to catch a break from the fast-moving digital world and to give your eyes a rest from flickering computer screens," said Ms Suppa.