WATCH: 2021 Mercedes-AMG ONE previewed

Testing of the advanced 746kW Mercedes-AMG ONE is well underway and, to prove it, the German car-maker has released a short video of a late-stage prototype testing on track.

Turn the volume up and, for the first time, you'll also be able hear the 1.6-litre V6 hybrid being worked hard for its living as the automotive technical tour de force is driven in front of the cameras for the first time.

Claimed to "sound pretty much the same" as a Formula 1 race car by a man who should know, current F1 world champion Lewis Hamilton, the video of the $5 million hypercar in action proves how far down the road AMG engineers are to launching the much-delayed ONE in 2021.

In the video, the mule being driven features some key differences to the original concept.

The bonnet intake is exposed while at the rear of the car there is a new rough-looking quad-tailpipe exhaust – both are expected to change for the production car that will arrive in 2021.

Inside, a version of the race seats is expected to stay, but will get a full retrim along with the rest of the interior that will look far more luxurious in the finished item.

Twin-lightweight display panels will also join the party with a third screen used to display the reversing camera's view. The same screen will also act as a rear-view mirror.

Both the dominant dorsal fin and cool scissor doors will be transferred to the production car.

Capable of a top speed of more than 350km/h, the Mercedes-AMG ONE is claimed to be able to hit 100km/h in less than 2.5 seconds and, astonishingly, destroy the dash from 0-200km in less than six seconds.

All this from a hypercar that can travel up to 25km on pure-electric power alone, making the Mercedes-AMG the perfect petrol-powered hypercar for billionaires with an environmental conscience.

Most, though, will snap up the world's most advanced hypercar because of its powertrain, which is a development of the 2014 F1 championship-winning V6 hybrid capable of spinning to more than 11,000rpm.

Created to go head-to-head with the Aston Martin Valkyrie, which is powered by a large capacity naturally-aspirated electrified V12, the ONE not only has an advanced turbo set-up and adopts not one but four electric motors, providing all-wheel drive.

Mercedes-AMG has already revealed one of the electric motors will drive an electric turbocharger to rid the tiny 1.6-litre engine of turbo lag, while another will be linked to the crankcase to assist the small V6's mid-range torque.

The crank e-motor alone is claimed to boost power by 120kW, while the two motors that drive the front axles raise the towering total power output by another 120kW a piece.

Those electric motors are fed current by battery packs mounted within the chassis behind the front axles and recharged on the move by energy clawed back through the front wheels. The ONE is said to be able to reclaim up to 80 per cent of braking energy.

The rear wheels, meanwhile, are driven by the F1 engine through a new eight-speed transmission.

Like an F1 car there is a qualifying mode that ramps everything up to max power for the lowest possible lap time.

Helping balance big downforce with low drag, the ONE will also benefit from motorsport-derived active aero.

Rumoured to weigh around 1000kg, the ultra-lightweight Mercedes-AMG hypercar is almost entirely made of carbon-fibre composites and comes with kilo-cutting carbon-ceramic brakes and in-board pushrod suspension that looks lifted from Hamilton's company hack.

Mercedes-AMG has already confirmed it plans to make only 275 ONEs – with eight left-hand drive cars confirmed for Australia.

Back in August the ONE made headlines when the sold-out run of cars was hit with delays linked directly to the introduction of stricter WLTP emission regs that demanded a particulate filter being implemented to the hybrid V6.

Engineers were also said to be grappling with the fragile nature of converting a highly-stressed F1 engine, which will have a service life of just 50,000km, car to road use.