With a hopeful eye on the approaching World Cup, Japan's embattled TV makers are hoping the key to their rescue can be found on the second floor of Bic Camera's downtown Tokyo outlet.

Sales of big-screen televisions with super-high definition 4K technology are picking up at the nationwide electronics retailer, and their fatter profit margins are offering a lifeline to one-time industry giants Sony and Panasonic.

Retailers report that demand for the cutting-edge technology -- with four times the resolution of standard HD sets -- has surged sports fans shell out big bucks with the football World Cup kicking off in Brazil on Thursday.

"Many customers are coming to buy a new TV set because of the World Cup," said Daisuke Kogure, visual products floor manager at Bic Camera's Yurakucho outlet.

In a corner of the store devoted to 4K screens, crystal-clear images of footballers and flowers show off the new technology.

"Even though commercial broadcasting is still to come, customers are still interested in seeing photo images and movies on 4K television screens," Kogure added.

On Monday, a consortium of major Japanese broadcasters, TV manufacturers and communications firms began test broadcasts of satellite television programmes in 4K across the country of 128 million, with some World Cup games set to be shown.

The move comes with Tokyo's backing as it looks to boost the competitiveness of the world's number three economy -- neighbouring South Korea is already testing 4K technology for cable programming.

Sony president Kazuo Hirai recently pointed to the ultra-high-definition technology as a possible saviour for the company's money-losing TV unit, which has bled about 790 billion yen ($7.8 billion) over the past decade.

Hirai's efforts to drag the TV business into the black have so far failed, but he has repeatedly shrugged off pleas to abandon a division that he insists remains central to Sony's core business.

- 'Great quality, limited programmes' -

Sony's rivals Panasonic and Sharp have also suffered massive losses in their TV businesses, although their units are recovering as they look to go on the offensive with high-end televisions.

The Japanese giants have been hammered by razor-thin margins and ferocious competition from overseas rivals, particularly in South Korea and Taiwan.

Panasonic and Sharp have both said they will boost their lineup of 4K televisions and computer monitors, while Sony, a world leader in the technology, is also eyeing the booming health field.

It is hoping that a tie-up with Olympus -- best known as a camera maker but which also makes medical equipment -- will usher in endoscopic 4K images that can better diagnose diseases.

But persuading enough consumers to embrace the cutting-edge technology could still be a struggle.

Sales of 4K-equipped TV sets remain a small fraction of sales of LCD flat screens. And while the average price of 4K TVs has dropped to 330,000 yen ($3,300) from 491,000 yen a year ago, the technology is still expensive and offers limited viewing options.

"The success of 4K television will depend on the richness of its content," said Eiji Mori, analyst with Tokyo-based research company BCN.

"So far what's available is just test broadcasting, and it's unclear when private broadcasters will start supplying 4K-quality TV programmes," he added.

And the planned rollout of next-generation 8K technology -- offering quadruple the resolution of 4K -- for the 2020 Olympics in Tokyo could also hold sales back, Mori said.

"Broadcasters have to decide whether investing in cameras and editing equipment for 4K programmes can pay off in just a few years," he said.

"There is also a question about whether consumers will choose 4K televisions when they buy one with a 50 inch-display or larger."