This is the shocking moment a modified motorcycle accelerated uncontrollably during a test drive.

Suphachok Thaweechoti created a customised mini-bike, but when he attempted to test the engine, the vehicle went haywire in Bangkok, Thailand.

Footage shows Suphachok welding the frame of the two-wheeler and painting it yellow before installing the engine on December 21.

He then fitted the tyres and calibrated the brakes and chain, completing the DIY project by mounting a mosquito racket as a makeshift headlight.

In another clip, Suphachok can be seen pulling the starter cord repeatedly to kickstart the motor.

Moments later, the engine roared to life, sending the bike bolt away uncontrollably while the enthusiast was left chasing it.