A consortium of bus operators, power companies and green groups on Tuesday urged the government to expedite the replacement of diesel buses with ones that run on clean energy.

The Zero Emissions Mobility Consortium said concrete action is urgently needed to tackle a dangerous level of roadside air pollution in Hong Kong as well as the climate crisis.

The CEO of Clean Air Network, Patrick Fung, said the government should discuss with bus and energy companies to come up with a comprehensive roadmap for replacing all diesel buses.

"When we talk about viability, I think we'll talk operationally, technologically and financially... Without this done, we will only achieve a certain limited scale of transitioning... that is not an ideal situation," he said.

The group said authorities should speed up and expand trials for both electric buses and hydrogen fuel cell buses, and amend regulations to facilitate the adoption of these zero emission buses.

The Executive Director of Civic Exchange, Lawrence Iu, added that the government should do more to control the number of private cars in Hong Kong, including introducing congestion pricing.

"Cost-wise... to buy a private vehicle in Hong Kong is relatively cheap compared to renting a car park or paying the gasoline. That's likely to encourage people to buy their own private vehicles to enjoy the really comfortable environment no matter on a really efficient road or a seriously congested road," he said.

He pointed out that the sweltering heat that the city is experiencing shows it must take action to address climate change.