Toyota's next-generation Prius is one of the most eagerly-awaited green cars of the moment, but potential buyers may have to wait a little longer to get their hands on the car.

According to Automotive News, Toyota has pushed the next-gen Prius's production date back by six months, from next Spring to December 2015.

That's likely to set back the car's launch date by a similar amount, while production of the plug-in model is still scheduled for October 2016.

It isn't clear what exactly has caused the half-year delay.

A source for Automotive News suggests that engineers are performing extra tweaks to the car--perhaps to maximize fuel economy, or to fix body or chassis issues.

Such delays aren't uncommon in the automotive industry, and as one of Toyota's most important models--a figurehead for its drive for cleaner vehicles--Toyota will want to make sure it gets the new hybrid right from the start.

The current model has contributed significantly to Toyota's tally of over six million hybrid sales worldwide, since the very first Prius hit the Japanese market back in 1997.

MORE: Next Toyota Prius Hybrid To Have More 'Heart-Racing' Design?

Toyota's hybrid expert Satoshi Ogiso says the next Prius will be a "test bed of critical new technologies", including the next generation of Toyota's hybrid system and the all-new platform--a modular setup likely to underpin several Toyota models in future.

The Japanese firm is taking a very different route to greener vehicles from rival Nissan, putting its faith in hybrid and fuel-cell vehicle technology rather than electric cars.

Toyota recently unveiled the final design for its fuel cell sedan, not far removed from the concept vehicle seen on auto show stands over the past few years.

That vehicle is scheduled for a "before April 2015" launch date, and it's likely some elements of the car's styling will find their way into the next Prius. The Prius, however, is expected to keep the traditional "Prius shape".

A more conventional dashboard than the current love-or-hate interior is also likely, while Toyota is targeting a ten percent economy improvement: bank on an EPA-rated 55 mpg when the car eventually hits the U.S.


Follow GreenCarReports on Facebook, Twitter and Google+