Motorola has thrown its hat into the folding smartphone ring with a revamped version of its Razr flip phone that was first launched 15 years go.

The new model of the same name, which will launch in the US in January 2020, mimics the recognisable shape of the 2004 original with a cover that flips up to reveal the screen.

But instead of a keypad and 2.2 inch display, the inside is entirely made up of a continuous, 6.2 inch OLED touchscreen display.

Made of flexible plastic, the display bends in half without the visible seam that marks similar folding screens such as Huawei's Mate X and Samsung's Galaxy Fold, according to Motorola.

Powered by two small gears, this mechanism leaves little to no gap between the two halves of the screen when folded, to prevent debris and dust from entering.

Another feature that sets the Motorola apart from other models, is the fact that it folds horizontally rather than vertically, to roughly the same thickness as the original Razr at 14 millimetres.

It also transforms from a palm-sized devices into an average-sized smartphone, rather than opening from a regular phone into a tablet.

The exterior consists of stainless steel and glass, topped off with a smaller "Quick View Display" that can be used to show notifications, control music and take selfies with the front-facing camera.

Even the hallmark "chin" of the original Razr is kept, but kitted out with an additional fingerprint reader, four-speaker system and USB-C port.

Motorola has described the phone as "design-first" as evidenced by its mid-range six gigabyte RAM, 128 gigabyte storage and Snapdragon 710 chip.

Foldable screens have been dominating the smartphone world this year, with most major players sharing their take on the trend.

Beyond Samsung and Huawei's high-profile launches, Microsoft unveiled the two-screen Surface Duo – which can be opened like a book and used like a game controller – while Energizer debuted its Power Max P8100S, whose specs are "better than many people's laptops".