Large parts of the world are not ready for zero-emission vehicles, which is why Toyota did not sign a pledge this week to phase out fossil-fuel cars by 2040, the world's largest car maker has said.

Six major carmakers, including General Motors, Ford, Sweden's Volvo Cars and Daimler Mercedes-Benz, signed the Glasgow Declaration on Zero Emission Cars and Vans.

A number of countries, including India, also signed the pledge.

But Toyota and the world's second biggest car maker Volkswagen, as well as crucial car markets the United States, China and Germany did not.

A spokesperson for Toyota told Reuters that where the energy and charging infrastructure, economics and customer readiness exist, "we are ready to accelerate and help support with appropriate zero-emission vehicles."

"However, in many areas of the world such as Asia, Africa, Middle East an environment suitable for promoting full zero emission transport has not yet been established," the spokesperson said.

"We think it will take more time to make progress - thus, it is difficult for us to commit to the joint statement at this stage," the spokesperson added.

According to a study published by the Munich Mobility Show in April, there are huge global disparities in electric vehicle ownership.

Sales are soaring in the European Union, China and the US, but cumulative electric car registrations during 2020 in South America, with a population of more than 420 million, were below 18,000.

And registrations in Africa, home to 1.2 billion people, were exclusively in South Africa and totaled just 1,509 cars in 2020.

Volkswagen also said the tempo of electric vehicle adoption would "vary from region to region" and chief executive Herbert Diess dismissed the zero-emission pledge at the COP conference earlier this week.

"It could still make sense to use synthetic fuel cars in Latin America in 2035," Diess said.