The upcoming Mercedes-AMG C53 4Matic has been spied undergoing cold-weather testing for the first time, less than a year before it's planned to head into UK showrooms alongside standard versions of the new, fifth-generation C-Class.

Set to directly rival the Audi S4 and BMW M340i xDrive, the four-wheel-drive C53 will replace the existing C43 4Matic. It forms part of an extensive new C-Class line-up from AMG alongside successor models to today’s C63 and C63 S – each to be offered in saloon, estate, coupé and cabriolet body styles.

Despite its extensive disguise, the C53 prototype pictured here is clearly differentiated from standard versions of the new C-Class we’ve already caught testing by a series of typical AMG styling elements, including a 'Panamericana' grille with vertical louvres, a deeper front bumper assembly with new vertical ducting and so-called flics within the outer edges, wider sills and a bespoke rear bumper housing four round tailpipes.

It also sports large brake discs and what appear to be six-pot front brake calipers – a telltale sign that this is no ordinary C-Class. Further differentiation from previous fifth-generation C-Class prototypes include 18in wheels, those up front featuring an open-spoke design and those at the back with solid spokes.

As first reported by Autocar last year, AMG has settled on a four-cylinder strategy for its new C-Class models.

The C53 is planned to eschew the turbocharged 3.0-litre V6 petrol engine of the existing C43 for a further developed version of the turbocharged 2.0-litre four-cylinder petrol engine already used by the A35 and its more powerful A45 sibling.

Nothing is official just yet, although indications are it will be tuned to develop in the vicinity of 380bhp, giving the new C53 and subtle 13bhp increase in power over the outgoing C43.

Along with the new engine, the new AMG model is set to adopt a nine-speed automatic gearbox and heavily updated four-wheel drive system offering a greater apportioning of drive front to rear.