BROWNSTOWN, Michigan, Jan 25 (Reuters) - General Motors and Honda have begun shipping fuel cell power systems to customers from a factory near Detroit, they said on Thursday, a new test of whether hydrogen power technology can achieve mass-market success.

Initial production of fuel cell power units will be relatively small, with Honda executive Jay Joseph saying at an event on Wednesday that his company is aiming to deliver 2,000 fuel cell power units annually by the middle of this decade.

Honda will use fuel cells in a version of its popular CR-V sport utility vehicle due to be unveiled in March, and Joseph said they will also be included in other products including stationary power generators.

The company and Japanese truck maker Isuzu are developing a hydrogen-fueled Class 8 semi truck.

GM has previously announced plans to supply fuel cell systems to commercial truck maker Autocar and heavy mining and construction equipment maker Komatsu, and is marketing fuel cells under the Hydrotec brand.

The company has worked on fuel cells as an alternative to combustion engines for nearly 60 years. Its CEO Mary Barra said in 2021 that the automaker was developing a medium-duty commercial truck that would use fuel-cell power.

Charlie Freese, executive director of GM's Global Hydrotec operation, declined to discuss production volume targets or timing for a GM fuel cell truck at an event on Wednesday.

Rival automakers including Hyundai, Toyota, Stellantis, Daimler Trucks and U.S. startup Nikola are pushing to develop commercially viable fuel cell technology as a replacement for diesel motors as tougher clean air standards threaten combustion technology.

Fuel cell technology offers the promise of replicating the hauling power and fast refueling of heavy diesel engines in ways batteries cannot match.

But it has failed to break through despite government subsidies and incentives because of the high cost of the systems and a lack of hydrogen refueling infrastructure.

To support commercial production at the GM-Honda joint venture, "we are trying to work with customers that have the ability to do centralized refueling", Freese said. (Reporting by Joseph White; Editing by Jan Harvey)