“We just couldn’t get to the point where we could have enough batteries to get to the payload that we knew we needed,” CEO Stephan Hanvey said of the choice to switch to hydrogen power.

It would be flown by an on-board pilot using a pair of joysticks, but the technology exists to eventually fly it remotely and even autonomously, Mr. Hanvey said.

Kai joins a rapidly expanding sector populated by many aeronautics firms, including Boeing and Airbus but few are focusing on the use of hydrogen fuel-cells - with the majority using electric motors.

Prototypes from Boeing and Airbus made successful test flights earlier this year, according to Vertical Flight Society, an industry group.

Most alternative options are powered by batteries, which can add a lot of weight and limits the function and range of them.

Skai's use of hydrogen fuel cells means it is much lighter than others and this allows for more flexibility in its use.

'We just couldn't get to the point where we could have enough batteries to get to the payload that we knew we needed,' CEO Stephan Hanvey said of the choice to switch to hydrogen power.

Hydrogen fuel cells create electricity to power a battery and motor by mixing hydrogen and oxygen.

The only emissions are steam and water and excess energy can also be stored in batteries.

Alaka'i says it's planning a test flight near its Massachusetts headquarters.

It would be flown by an on-board pilot using a pair of joysticks, but the technology exists to eventually fly it remotely and even autonomously, Mr Hanvey said.

It will be years before the Federal Aviation Administration allows the autonomous flight of passenger vehicles, said attorney Thaddeus Lightfoot, a partner with the firm Dorsey & Whitney who helps companies navigate FAA rules.

Regulators are still grappling with the proliferation of smaller drones - those under about 50 pounds flown by hobbyists and filmmakers.

The FAA just this year eased restrictions on flying small drones over crowds and at night.

Drone-like vehicles such as the Skai must first simply prove their airworthiness, like any common plane, Mr. Lightfoot said. After that, getting commercial certification is another convoluted process, he said.

A transportation company is betting its sleek new hydrogen-powered electric flying vehicles will someday serve as taxis, cargo carriers and ambulances of the sky, but experts say they will have to clear a number of regulatory hurdles before being approved for takeoff years in the future.

With six rotors on the roof and seats inside for five people, a passenger model of the Skai (pronounced “sky”) unveiled near Los Angeles resembles an oversized drone crossed with a luxury SUV.

Like a drone, the vehicle from Alaka’i Technologies takes off and lands vertically. It’s one of many similar electric flying crafts in production, including prototypes from Boeing and Airbus that made successful test flights this year, according to Vertical Flight Society, an industry group.

Most are powered by batteries, which can add a lot of weight. The Skai instead uses very light hydrogen fuel cells to run its rotors, giving it a range of 644 km and the capacity to carry 454 kilograms in people or freight, the company says.

Skai, a hydrogen-powered 'flying car' for taxi, ambulance and cargos.