* Hydrogen seen as alternative for fossil-fuel hungry planes * Startup has flown 10 hydrogen plane test flights * California-based firm raised $34.4 million so far * Firm plans to move from propeller planes to jets (Adds new funding from British government) LONDON, Dec 16 (Reuters) - Hydrogen plane startup ZeroAvia said on Wednesday it had secured $37.7 million in new cash via a funding round led by Bill Gates’ Breakthrough Energy Ventures and from the British government to support its bid to develop zero-emission aircraft. Backers for California-based startup, which has completed 10 test flights with a six-seater propeller plane powered by hydrogen, now include Amazon and energy giant Royal Dutch Shell, which both joined the funding round. Hydrogen, which produces water when it burns, is seen as a potential alternative for the aviation industry, a major user of fossil fuels. Hydrogen can be made from fossil fuels or from water using electrolysis, although this is an expensive process. “This is a capital-intensive industry, so having investors to help you through the process is very important,” ZeroAvia Chief Executive Val Miftakhov told Reuters, saying a plane was “a power-hungry machine, especially on take off.” ZeroAvia, which has been conducting test flights in Britain, aims for commercial flights of up to 500 miles using 10- to 20-seat aircraft by 2023 and commercial jets able to haul up to 200 passengers 3,000 miles by 2030. Miftakhov said his startup expected to have planes for cargo flights in operation before commercial passenger planes. The funding round led by Breakthrough Energy Ventures raised $21.4 million, while British state support amounted to $16.3 million. ZeroAvia has now raised a total of $49.7 million since its launch and will use the latest cash to scale up its technology for larger aircraft. It has teamed up with British Airways to explore how the carrier could shift to hydrogen-powered planes in future. Amazon’s backing comes from its $2 billion Climate Pledge Fund. The online retailer, which aims to run a carbon neutral business by 2040, has ordered electric vans from Daimler AG’s Mercedes-Benz and startup Rivian. Shell’s funds came from its Shell Ventures a unit which has been boosting investments in solar and other renewables. Hong Kong-based venture capital firm Horizons Ventures was also among the investors.