The rival handset-tablet hybrids have contrasting designs.
Huawei's Mate X places its fold-out screen on the outside of the device, so that it covers the front and rear of the phone when closed.
In both modes, the display is larger than Samsung's. Huawei's device is also flatter and thinner when shut.
The Mate X's screen is 8in (20.3cm) when unfolded and larger screen is 6.8in when closed.
The device was priced at Euro 2299 amid gasps of the audience.