Even though these images were taken at very long range, the styling is clearly very heavily influenced by the look of the new S-Class and A-Class.
A wide grille dominates the C-Class’s front, with a large three-pointed star emblem at its centre. This is flanked by a pair of oversized headlights that give the new C-Class a more aggressive look. The lights will use LED technology inherited from the latest E-Class models.
At the back, thicker C-pillars and a more sculpted boot both mirror the look of the new S-Class flagship while a pair of slender twin exhausts are neatly integrated into the rear bumper.
Taking on the current BMW 3 Series and Audi A4 will be no easy task but Mercedes has a wide range of models planned.
Bookmark this page as we will be regularly updating it with the latest news on the new C-Class.
New C-Class release date
The C-Class will be unveiled in early 2014 - possibly at Detroit Motor Show in January. A probable release date would be summer 2014 - alongside the C-Class estate.
New C-Class engines and specs
Expect a range of ultra-efficient petrol and diesel engines including a four-cylinder engine developed and built by Nissan - the first engine built in the U.S. to be used in a mainstream Mercedes - while a plug-in hybrid model is also planned to help take on the new Lexus IS 300h.
Mercedes will build the car on a new modular architecture called MRA, that will allow the firm to offer its 4MATIC four-wheel drive system on right-hand drive cars for the first time, to compete with Quattro-equipped Audis and xDrive BMWs.
Expect to see big updates to the amount of safety tech onboard, too, with the new C-Class borrowing systems from the current E-Class. This includes cameras that can detect traffic at junctions, and the ability to steer itself in traffic jams.
New C-Class Cabriolet
Our spy shots also prove Mercedes is working on a C-Class Cabriolet. Effectively a replacement for the CLK, the C-Class convertible is expected to go on sale in 2015 - a year after the new saloon is scheduled to arrive in UK showrooms.
Despite heavy camouflage, the cabriolet's sleek profile can clearly be seen, although it's impossible to tell at this stage whether Mercedes is planning to use a fabric roof, or a folding hardtop. Judging by the compact rear end, though, a fabric roof - that's both lighter and cheaper to produce than a metal one - seems most likely.
According to inside sources, an A-Class cabriolet is no longer part of Mercedes' product plan, so this car, although slightly larger, will rival the Audi A3 Cabriolet (which is based on the A3 Saloon) and the new BMW 2 Series Convertible - both due in 2014. It's also likely to start from under £30,000, making it the most affordable convertible in the Mercedes range.
A C-Class Coupe is also expected in 2015.
Mercedes C63 AMG
Our photographers have also spotted the new C63 AMG testing ahead of its 2014 release date. The images in our gallery show it sporting bigger, chunkier bumpers, large alloy wheels and twin exhaust housings at the rear.
Unlike the present car, with its 6.3-litre V8, the new C63 will be powered by a more efficient 5.5-litre twin-turbo V8. It is expected to have the same 518bhp output as the E63 and CLS 63, which also use the newer turbocharged engine. That’s a jump of 67bhp.
It will also have the same AMG-tuned seven-speed MCT automatic transmission, which along with retuned adaptive suspension, stronger brakes and less weight should help it improve on the current C63 AMG’s 4.5-second 0-62mph time, while using less fuel.
Meanwhile, a four-wheel drive C63 AMG is considered. AMG’s senior powertrain engineering manager, Dr Jorg Gindele said: “Yes, a C63 is possible. There is one car already [a prototype at AMG's headquarters in Affalterbach, Germany]. I know this because it’s my car!”
A new six-cylinder BMW M3 will make its debut in 2014, and the competition between the two is expected to be fierce. The C63 AMG will cost £56,000 when it arrives in showrooms.