European aerospace giant EADS on Sunday unveiled its "Zero Emission Hypersonic Transportation" (Zehst) rocket plane it hopes will be able to fly from Paris to Tokyo in 2.5 hours by around 2050.

"I imagine the plane of the future to look like Zehst," EADS' chief technical officer Jean Botti said as the project was announced at Le Bourget airport the day before the start of the Paris International Air Show.

The low-pollution plane to carry between 50 and 100 passengers will take off using normal engines powered by biofuel made from seaweed before switching on its rocket engines at altitude.

The rocket engines, powered by hydrogen and oxygen whose only exhaust is water vapour, propel the plane to a cruising altitude of 32 kilometres (20 miles), compared to today's passenger jets which fly at around 10,000 metres.

"You don't pollute, you're in the stratosphere," Botti said.

To land, the pilot cuts the engines and glides down to Earth before reigniting the regular engines before landing.

EADS hopes to have a prototype built by 2020 and for the plane to eventually enter service around 2050.

The project is being developed in collaboration with Japan and uses technology that is already available.

A four-metre model of the plane, which looks similar to the now defunct Concorde supersonic jet, will be on show at Bourget for the biannual aerospace showcase which begins on Monday and opens to the general public on Friday.

Picture: A computer-generated image from the European defense group EADS shows the so-called "Zero Emission Hypersonic Transportation" (Zehst) rocket.