A double-decker hydrogen bus made its maiden cross harbour journey on Sunday, with route 170 passing through three toll tunnels, including Aberdeen Tunnel, Cross Harbour Tunnel and Lion Rock Tunnel.

Richard Hall, the managing director of Citybus, said the company aims to phase out diesel buses in the next few years with plans of operating a full fleet of zero-emission buses by 2045. He said the company plans to purchase a large number of electric buses and bring in at least five hydrogen buses.

"By running those vehicles in parallel, we have a greater volume. We will be able to get more data that will enable our future design and purchasing decisions. In terms of fares, fares have to rise on an ongoing basis. Fares are critical to supporting the sustainability of our operations," he said.

"Fares ensure that our employees, citizens of Hong Kong... can meet their cost of living and continue to keep pace with inflation. Fare increases also allows us to invest in new technology, improving our bus operations and delivering a great solution to all the citizens of Hong Kong that they can be proud of."

Hall said their fleet composition in the future will compose of 70 percent hydrogen buses and 30 percent electric buses. He also said that Hong Kong would be put at the forefront of international and technological development for new energy solutions.

Some people were already queuing at Wah Fu Bus Terminus at around 6am to board the first scheduled bus of the day. A man surnamed Wong said he is worried about travelling through tunnels in a hydrogen bus given that it is flammable, but he said he believes the company had undergone many tests before its release.

"Diesel buses run on diesel so it releases a lot of exhaust smoke, and the bus is pretty loud when it is running. The hydrogen bus is a lot quieter and you can only hear the sound of the air conditioning. It is quiet inside and out," said another passenger surnamed Yau.