Busy traffic, loud noise and constant passers-by? Not a problem for these cats.

Four-legged "assistants" can be found perched in certain shops across Hong Kong, keeping a nonchalant eye on business while the city does its non-stop bustle past their storefronts.

Their presence has inspired Dutch photographer Marcel Heijnen to make them the subject of a book and recent exhibition -- capturing their unique characters in some of the city's most traditional neighbourhoods.

The pictures show cats of all shapes and colours: masters of their domains whether on sacks of goods, atop countertops, or almost blended into displays.

"Well, they're very chilled, They're very zen. They see people coming in and out every day, they have trucks unloading, people walk around with boxes, they're very unfazed, they sit on top of everything," said Heijnen.

None are as famous as Hong Kong's celebrity shop cat -- Cream Brother.

The British Shorthair has nearly 200,000 followers on Facebook and draws masses of fans, including when his shop closed in 2016.

He is also behind several books, has starred in advertising campaigns and has his own "Cream Bro" foundation that helps less fortunate felines. Now somewhat semi-retired, he still has regular visitors.

"I think he is a very special cat, very handsome, very cute," says Solid Ng, a bank teller who visits him twice a week at home.

Such fame was unexpected, says his owner Ko Chee-shing, but it's a life that came naturally to the former convenience store cat.

"His character is really like a star. He would sit down and let you photograph him. Everyday there were hundreds of people coming to our store to take photos of him, he would stand up and pull a cute face, or just sleep and let people take pictures of him."

For Heijnen, the photographs also point to a nostalgic pause in a constantly changing city.

"I think the uniqueness in the photographs is that it captures the background," he said, while a favourite subject sat on boxes piled on goods in the background.

"So it's not just about cats, it's about the stores and in many of my photos you see that... 90% of it is the store and the cat is very small. And these are very traditional stores, they're very timeless. These photos could have been taken in the 60s."