SINGAPORE - Colouring books are no longer just for kids.

More adults here are turning to colouring as a relaxing and creative hobby.

This latest trend is sparked by the worldwide success of Scottish illustrator Johanna Basford's Secret Garden, an adult colouring book that has sold more than 1.5 million copies in 24 languages since it was published in 2013.

In Singapore, two illustrators have jumped on the bandwagon, creating their own colouring books with a touch of local flavour.

"The inspiration behind my books are mainly the landmarks that I like. For instance, Fullerton Hotel. I turned it into a Lego building, where toys are having fun playing with the lego and use it to form the Fullerton Hotel," said 48-year-old artist William Sim.

Demand for Mr Sim's first book, Colouring The Lion City, proved to be a success, making its way into the bestseller list for local non-fiction books.

Sales for digital marketer Sofy Rahman's Coloursutra series also surpassed her expectations.

The 32-year-old sold almost 300 books locally on Amazon.com, and has since launched a second book on Oct 31 based on the Singaporean love of food.

"For the second book, I realise that food is very relatable to people. They find pleasure in it. So I decided to incorporate food and colouring together and include quotes to go along with the whole design," said Ms Sofy.