Hybrid cars don't have to be expensive to make, Toyota told Reuters as it showed off the production site of its petrol-electric hybrid cars for the first time on Thursday.

The news agency noted that many leading car makers, including General Motors, had quite recently questioned the benefit of developing hybrid cars, arguing they are merely an interim solution before zero-emission fuel-cell vehicles take over.

According to Reuters, they accused - possibly accurately - Toyota and Honda, the only other mass-producer of petrol-electric hybrid cars, of selling them at a loss given the labour-intensive assembly required.

There may have been some truth to that argument before, but no longer, Toyota told Reuters - the company launched its second-generation Prius hybrid sedan in Japan last month.

"We used to build the previous Prius on an exclusive assembly line at the Takaoka plant, and later at Motomachi," Kenji Takahara, head of administration at the neighbouring Tsusumi plant, which now builds the Prius, told the news agency, adding: "Now, it shares a line with four other mass-production sedans."

Reuters said that is a big and necessary step for Japan's top car maker as it aims to offer the hybrid option on most of its models in the not-too-distant future - Toyota hopes to sell 300,000 of the fuel-efficient vehicles a year from mid-decade.

The news agency said visual comparisons with the production method for the previous Prius, launched in late 1997, are difficult because journalists were never allowed to visit the assembly site, but the numbers speak for themselves: the Prius's current assembly line rolls off about one car every minute, compared with one every eight to 10 minutes for the previous model, and, although it needs to pass through 11 extra line stations during assembly compared with a regular car, productivity has improved by at least 15% for the current model.

Reuters said a factory tour showed it is difficult to tell there's any difference between a hybrid and a conventional car.

"The worker is installing the hybrid engine system into the Prius just like a regular gasoline engine," assembly manager Yoshihisa Nagatani proudly told Reuters, pointing at the shell of a Prius hanging on an overhead conveyor belt as it followed a Camry.

In addition to some tweaking of the assembly line required with any new model launch, mixed assembly has been made possible by the huge increase in projected sales, Toyota told Reuters.

Reflecting their new-found popularity - sales are currently running six times ahead of forecast, every other car on the five-model assembly line at the Tsutsumi plant is a Prius, the report noted.

In contrast, rival Honda told Reuters that low volumes are forcing it to practically hand-build its Insight hybrid coupe model, much like the NSX and S-2000 sports cars while Japan's second-largest car maker has admitted that, after four years of selling hybrids, it barely makes any profit on them.

Reuters said that Toyota's feat in mass-producing its hybrid car should be an encouraging sign for other rivals as they follow Japan's top two car makers into the market.