Popular ride-hailing app Uber has dropped the "U" from its app icon as it unveiled a new look and logo early on Wednesday (Feb 3).

The new designs were inspired by "the story of bits and atoms", respectively the building blocks of technology and the world, Uber's chief executive and co-founder Travis Kalanick wrote in a press release on Uber's website.

Mr Kalanick was personally involved in much of the rebranding, Wired reported. Forcing himself to learn about design concepts, Mr Kalanick told Wired: "I didn't know any of this stuff. I just knew it was important, and so I wanted it to be good."

At "the heart" of the new logos for the rider and partner apps is the "bit"- essentially a square - with shapes and patterns surrounding it. The old logo was "somewhat distant and cold", Mr Kalanick said.

Reaction from users on Twitter has been mixed, with some expressing their dislike for the new logo.

The new Uber look will also include colours and patterns tailored after the different cities and countries the service operates in.

"Every city has its own character and our long term goal is to have unique designs for cities as well as countries. This will mean adding hundreds more colour palettes and patterns over time," Mr Kalanick wrote in his press release.

Uber currently operates in 68 countries, and transports food and packages in certain countries, as well as people.